Language McRantypants Strikes Again (Obscure Detail Division)

OK, so... I'll buy that the character signs. Really, he has so many language skills, it wouldn't surprise me to find that he knows sign. However -- and this is the kicker -- he'd know American Sign Language. Not British Sign Language. I can get past the BrE spellings (kind of). I can get past (somewhat) the BrE phrases in the mouths secondary characters (even if they're not specifically identified as being from the UK). But... Ms. Writer Person, you're really pushing it when you put British Sign in the hands of an American character.

Grrrrr.