I made my spray in Paint, and just used Wally to make it a spray based on the picture I made...
I won't suggest my coolest idea (that is, after the one I have now, cos that's my old spray
However, I suggest you find yourself a picture you like, or a logo (that you change a little, as I did), and use that. Thereby, you can get a know logo, yet very personal.
For those who have seen my spray ingame; Imagine a swastika where I have the RR; and you'd call me a sick bastard...