The Court of Appeals cited the Restatement of Torts (a treatise articulating general principles of common law) for the definition of trespass to chattels:

> In accordance with Jones, the threshold question is whether chalking constitutes common-law trespass upon a constitutionally protected area.Though Jonesdoes not provide clear boundaries for the meaning of common-law trespass, the Restatement offers some assistance. As defined by the Restatement, common-law trespass is “an act which brings [about] intended physical contact with a chattel in the possession of another.” Restatement (Second) of Torts § 217 cmt. e (1965). Moreover, “[a]n actor may . . . commit a trespass by so acting upon a chattel as intentionally to cause it to come in contact with some other object.” Id.Adopting this definition, there has been a trespass in this case because the City made intentional physical contact with Taylor’s vehicle. As the district court properly found, this physical intrusion, regardless of how slight, constitutes common-law trespass. This is so,even though “no damage [is done] at all.” Jones, 565 U.S. at 405 (quoting Entickv. Carrington,95 Eng. Rep. 807, 817 (C.P.1765))

The Restatement explains, in Section 218, that liability for trespass generally requires some sort of injury or deprivation of use. So you can't sue someone just for touching your car. But it also explains in Section 217 that the trespass itself can occur absent injury or dispossession, and that trespass can have legal significance even if it is not directly actionable.

Yes, that's the argument. The challenge was to reconcile that with e.g. the practice of leaving a fingerprint on the tail light when a search would have been illegal.

Edit: toned down.

I'm responding to this point:

> Is there actual case law about someone being prosecuted for the trespass of putting chalk at the bottom of someone's tire? How about sneezing?

> What about leaving a fingerprint on someone's car ... which ordinary people do all the time?

The Court relies on the part of the Restatement that says a trespass has occurred when you intentionally touch someone else's chattel property. That doesn't answer your point, which is why I referred you to Section 218, which explains that a trespass, though it has occurred, is not actionable standing alone absent damages or dispossession. So even though touching someone's car is technically a trespass, it's not an actionable trespass so you wouldn't see lawsuits involving mere touching.

(As to your point about police leaving fingerprints--I've never heard of the practice. But my assessment would be that even though it's trespass, it's not actionable (no damages), and it's not a Fourth Amendment violation because it's not actually part of the search, but merely incidental to it.)

>As to your point about police leaving fingerprints--I've never heard of the practice

Hence the link in the comment I referred to: http://mentalfloss.com/article/502605/reason-police-officers...

>But my assessment would be that even though it's trespass, it's not actionable (no damages), and it's not a Fourth Amendment violation because it's not actually part of the search, but merely incidental to it

But it's done when the officer isn't allowed to (otherwise) search -- before he's had any contact with the driver or even looked inside the car.

You have to think of the causal chain that leads to recovery of evidence. Marking your tire with chalk is part of the causal chain--if the police didn't do it, they wouldn't know you had broken the law. Touching your car during a stop is not part of any causal chain--it's a separate tort that happens to be non-actionable because there is no damages.

Say a police officer stops you for running a red light. At that point, he has no suspicion that would justify a search. I tries to tap on your door to get you to roll down your window, and his ring scratches your car. That is a trespass to chattels, and it's actionable because it has resulted in damage to your car. After you roll down the window, he sees someone snorting cocaine in the back seat. He then searches your car, and recovers tens of kgs of drugs.

Was there an illegal search? No. Even though scratching your car was a trespass, and even though you can still sue for the cost of fixing the scratch, that trespass had nothing to do with recovering the evidence of drug crimes.

I appreciate the analysis of the cocaine detection, and the torts, but the question was about the evidential legality of touching your rear tail light. That was not necessary to conduct the stop and (by supposition) there is insufficient evidence for a search (beyond what he can ordinarily see), etc.

Are you saying that e.g. the cop's fingerprint on the tail light could not be used as evidence, because it was an illegal trespass?

Ah, okay, I get it now. In that case, I think the cop’s fingerprint could be used as evidence if the cop went missing. Say the cop opened your bag and dug through it without a warrant. That’s clearly a 4th amendment violation. That would result in exclusion of evidence obtained from the search of the bag. But if the cop went missing, fingerprints from the bag would be admissible as evidence of the fact that he had searched the bag and interacted with you. Whether the later search is legal would depend on the specifics of that search.

I'm trying to follow this discussion (because it is interesting) and I am a little lost about this fingerprint thing. What does leaving a fingerprint on a taillight accomplish for the officer?

From the link:

>Before cameras were installed on the dashboards of most police cars, tapping the taillight was an inconspicuous way for officers to leave behind evidence of the encounter, according to The Law Dictionary. If something were to happen to the officer during the traffic stop, their interaction with the driver could be traced back to the fingerprints left on the vehicle. This would help other police officers track down a missing member of the force even without video proof of a crime.

Ah, now I understand. Yeah, that's an interesting question.

It's actually quite straightforward. In Jones, the Supreme Court held that the 4th amendment protects people from invasions (i.e. trespass) of property rights without a warrant. You have a property right in chattels.[1] (That just means "personal property" as distinguished from "real property." The term is relevant because the rules for what counts as trespass are different between the two.)

A car is chattel property. Chalk-marking a car is a trespass to chattels, because it involves intentionally touching the car without permission. Therefore, under Jones, a warrant is required to chalk-mark a car in the course of investigating whether someone has broken the law (i.e. a search).

[1] The 4th amendment says: "The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated[.]" "Houses" are real property, while "papers, and effects" are chattel property.

It is by itself reasonable to mark tires, since doing so in no way damages the car and is less intrusive than other options law enforcement can constitutionally use (for instance, keeping a photographic record of every second your car was parked, which would not be a trespass, but would be far more intrusive).

But it's unconstitutional to do so, because the principle behind our laws say that law enforcement cannot (without a warrant or exigency) trespass on your property to accomplish its goals, whatever they may be.

The principle here seems sort of superfluous, but it's holding the line against any sort of trespass, some of which you'd probably find less reasonable, such as magnetically attaching a GPS transmitter to the bottom of your car.

    > ...but it's holding the line against any sort of trespass.

I just don't believe that practical solutions to real-world human problems is ever to be more strict, more pure, more rigid, more unwavering in the interpretations of rules(law).