Hinting that I'm bisexual to crush?

I have a crush on a sort-of friend at school who is bisexual and I need some way of letting her know that I am, too. I don't want to make a big deal out of it. My school and friends are very liberal and accepting, which is great but also makes it harder to be subtle, as even straight people can be pretty flirtatious with other girls, and very openly supportive of gay marriage and such. Even wearing a Stonewall sticker thing wouldn't really lead anyone to any conclusions, I don't think
Strangely, although she never told me she was bisexual, and only ever mentioned guys, I never had any doubt that she was, so either I have very good 'gay-dar' or she's very good at subtly letting people know. I only know she is for definite because I heard her tell someone else.

How can I tell her without being too subtle or making too big a deal out of it? I just want it to seem natural and relevant to the context, but how do I bring about that sort of discussion during an hour long Biology class?