The monarch did not pardon Turing, the monarchy did. Hence the signature was not that of the monarch.
Noting that Elizabeth was reigning when Turing was charged [ and later convicted and sentenced], there is some fair criticism - at least from the foundational American political perspective - that the lack of any personal acknowledgement of the injustice lessens the measure and the pardon's praise of its own beneficence, in light of its power to declare itself the very writ of pardon, is inexcusable.
Noting that Elizabeth was reigning when Turing was charged [ and later convicted and sentenced], there is some fair criticism - at least from the foundational American political perspective - that the lack of any personal acknowledgement of the injustice lessens the measure and the pardon's praise of its own beneficence, in light of its power to declare itself the very writ of pardon, is inexcusable.