The two triangles logo is a common (as such things go) symbol of bisexual pride. I did not invent it.
I did a rendering in Bryce 2 of that logo. You are welcome to make use of these if you like, I've provided three sizes below... The GIF files below were created from the larger Bryce rendering using Adobe Photoshop. (Both of these programs have later versions than that now, of course.)