If I were you, I would just humbly say that I am a young researcher in X field, and spend more time explaining my ideas. In my signature, I would just put something like PhD (ABD) or nothing at all. 

By the way, in my humble opinion, I don't think titles matter in academia. Researchers care more about mutual interests and your ability than positions. Putting the obligation of advising students aside, a professor would never refuse collaboration with a college student, if s/he is equally good as a PhD holder.