What almost all gals in a sorority do is put a sticker with their sorority name on the door. Being that both my former roommate and I are in the same sorority, there was no problem "distinguishing" who was in a sorority and who wasn't. Most people though just put the sticker beneath the peep hole of their door. Nobody worried about distiguishing who was in a sorority and who wasn't b/c it was pretty obvious and I guess nobody really cared to.
One of the girls down the hall from me last year was one of three in her room who was in a sorority. They had the sticker w/her letters beneath the peep hole and on the message board that was on their door, underneath her name, she had her letters.
Another popular thing to do is to make something on the computer with your name and clip art to hang on your door. You could incorporate your letters and colors into that.
Hope that helps some.
