This is true. Also, if you add hidden buttons that alter the way a data port works to either disable or enable it, or fry a device attached to it, this isn't intentional harm caused to police equipment specifically. It is a deterrent-after-the-fact, a protection, and a personal choice to modify one's own device without targeting anyone in particular and not intentionally, unexpectedly causing bodily harm.
the owner of the device could be charged with tampering with evidence. Signal is, paradoxically, an uninvolved third-party imho (technically uninvolved).
If Signal put this on their home page, in a sort of "download this to fuck with da police" advertising, maybe.
Judges aren't machines, that slavishly follow any tenuous reasoning. They're judging; it's in the name. Specifically, they have to judge your intent. In many cases American criminal law requires a 'mens rea', or 'guilty mind'
