Are there specific names for the signature images in the Ravnica guilds?
This Wizards.com article covers the aesthetics of the Return to Ravnica block, complete with an entire section ("Revisiting the Guild Symbols") on the changes made to each of the ten guild symbols since the original Ravnica block.  Nowhere in here are any names for the individual symbols given, and as this is the most in-depth official look at the symbols I've ever seen, it seems unlikely there are any official names.

EDIT: The only other official article I can find that really looks at the signets is this article from the end of the first Ravnica block (under "Ravnica's Best Guild Signets").  No names there either.