If you have photoshop this is how to do it:
1. Create a new document ranging from 2x2 to 10x10 pixels really.
2. make sure the background is transparent
3. zoom in as far as you can and get the pencil tool and draw a line from one side to the other, be it diagonal or across, your choice, your colour
4. edit > define pattern
5. on your new layer in the sig, go to blending options and put the pattern overlay on and have a play with what looks good.