The vulcan symbol with one less finger is either the shocker or the reverse shocker, both of which are already taken.

As for whether I am afraid of antis finding it, no. What could they do with it? There are some very remote scenarios where it could actually be an issue, but they are so unlikely that you are far better off worrying about other things. Most antis don't even dare step outside of cyberspace and the few examples of those daring enough to do so (Echols, Predator Hunter, etc.) were so socially inept that your instincts wouldn't have allowed you to respond positively to such an overture. What can they do if they know the sign? It's not something you are going to flash to more than one person at a time.