Each 2 colour combination has its own name and it's own picture used on cards that have both colours involved (generally in the background of the card text). Do the pictures themselves have a name other than just "Gruul Banner", "Rakdos Mask" or "Orzhov Eight Pointed Star"?
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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.