I don't approach others about it. On the other hand, I do make an effort to appear approachable to others, and generally act as friendly as possible. If I happen to end up talking to another trans woman and she brings up the subject, that's extra cool, but I don't expect it.
Also, I kinda have this mental filter where I assume everyone else is cisgender unless they specifically say otherwise. Basically, I do that to keep from reading people, and it helps with a lot of awkwardness. (Although, in one case, this has kinda funny results. There was a stranger in a sorta authority position, and I had to come out to her for a particular reason, and felt awkward. So I kinda didn't look her in the eyes until the subject came up, then finally brought it up about ten minutes into the conversation, and noticed she was really supportive and knowledgeable about it. Then I realized she was probably trans and I'd been worried for nothing, and at the end of the conversation she basically said she was. I felt a little silly.)