It seems there is a group of scientists who tirelessly attempt to prove that sexual orientation is biologically linked. Some Canadian scientists have found more proof that more gays are likely to be left-handed than are heterosexuals (Link to the article). Obviously, this does not mean that, if you are left-handed, you are more likely to be a gay/lesbian; but, it could be used as an alternative gaydar tool (?)
Some guys are apparently good at gaydaring with all their senses used like hyper-sensitive antennas to identify who is gay or not; but I am not. So, I sometimes need to rely on some other "superstitious" means like "left-handedness" etc.
In fact, I was once told that one way to identify whether a specific person you are observing (or happen to be observing) is gay or not is to look at his feet when he is sitting on a chair; if his heels are not on the ground (meaning he is lifting his heels -either left or right or both-, but his toes remain on the ground), then he is more likely to be gay. Don't ask me why, but this has actually worked in a number of instances. So, when you can't trust your gaydar, pay attention to his left hand and heels!