I've signed my name on a neg rep before and the person I repped actually gave me a positive reputation back. I don't think people will feel overly vengeful as long as you have something decent to say in your rep comment. I could be wrong though, since it's only happened once.
For positive reps I try not to sign my name (although I've done it a few times), because I don't want to get caught up in a "circle jerk", and I do feel that signing positive reps sometimes equates to soliciting reps. Having said that, at times I have appreciated when people sign their names in a "thank you" rep. It's just courtesy.
