I don't think the series I collect from give away my gender. However my beta name and gallery comments do. I think most of my favourite series have cross appeal.
I think I guess incorrectly most of the time, so I never like to assume. There was an ebay user who's name regulary pops up on auctions that I watch. From their user name and cel choices, I thought they were female. I dealt with "her" for the first time a few weeks ago and I was shocked when "she" was male. (I wanted to throw water over him to see if he turned back into a she
).