Hi!
I am unsure that there is any secret handshake, code words, or signals for us trans-women but some groups of trans-women may have invented them.
A pink, white, blue button or a true trans pin may be useful. If you go to a trans-women meeting though do not make assumptions there, as some ladies may be supportive cis-girlfriends and cis-significant others.
I too would never ask someone if she is trans. There is no stereotype look for someone who is MTF trans. Let them volunteer information as you would decide to open up.
I would also be respectful and kind to all, and a pretty smile does wonders.
Over time we continue to associate with people that are understanding and accepting. I suggest being safety minded and meet in public places and when you go to meet new people, and go with an accepting friend (who does not need to necessarily be trans) if at all possible. I would not suggest going alone, except perhaps to a public transconference or a open TG/TS support group in a public place.
Remember just because two people are both trans, their personalities and interests may be far apart. Be yourself always.
Hugs,
Chrissy