Look I get it, changing your profile pic is easy. It's a way to show support without actually having to go out and, you know, work at supporting something. I'm not saying it's bad, I'm saying that if you took the ten seconds out of your day to do that - think back and see where you took the next amount of time out to do something that might actually affect a change. This is a start, but please sit down for a moment and think about why you did it before you pat yourself on the back for being supportive.
There's really only two reasons for changing your profile pic to support a cause - because you want to raise awareness of an issue or because you want to let people know where you stand on an issue.
If the former, I doubt there's that many people who don't know that LGTB rights are an issue so who exactly are we trying to raise awareness in?
If the latter - if you're friends don't know where you stand on the defining civil rights issue of our generation - then you are doing something TERRIBLY wrong with your life and this is not the way to rectify that.
This kind of "activism" all too often takes the place of real people trying to make real changes happen. If you support LGBT rights, then write to your politicians, call them on the phone, organize or participate in a march in real life - because regardless of how much time we all spend online these communities are still seen as fringe by most people in positions of power.
Actively engage people in debate and stand so tall and proud on your principles that people can't help but acknowledge what you know is right.
This right here though? If this is all you're doing? Then this is just plain laziness.
So yeah, my two cents. There you have it.
(And as a sidenote, if you identify as an "ally" and are looking for a way to customize the pic, make it something "cool" or more indicative of you - then you are missing the point by such a wide margin I don't even know where to start.)