Let me make this statement up front because it seems that some people look for this kind of information: there isn't any "guaranteed" sign for someone who is gay, lesbian, trans-gender, or bisexual. Yes, some signs and aspects have more potential--but to label them here is pointless. It's pointless because as soon as I do it (and it's been written enough in astrology books on that subject), someone is going to label someone else--and I'm not going to join in that foolish game.
I've known many people from every sign who had partners from their own gender. It was their individual choice, and their respective signs were as different and unique as they were. Trying to identify them by a birth sign has no real bearing.
Again, I will say this: yes, there are several signs and planets in signs which have more potential for a gay lifestyle--just as there are some aspects and house placements which can possibly indicate such a choice. But I'd rather leave it to a formal discussion in an academic or professional environment for further qualification of those dynamics. In the meanwhile, be happy with the choices YOU make--because those are the only ones which should matter.