Some heterosexuals in college tried to come up with some sort of a sticker years ago (something different than the rainbow flag or pink triangle) to identify themselves as heterosexual (in part for flirting purposes and in part to take a stand).
I think they went with hot dogs and tacos (pink tacos for women, I don't remember the color of the hot dog, purple?).
NYC area talk-show host Andrew Wilkow (there's a thread here every Sunday for his Sunday show) has come up with blue diamonds. "Opposite" to pink triangles, and reflective of the concept that it takes TWO triangles to make a diamond.
I think I have it right.