Here, you got TeamViewer? I can help you via that if you don't understand this.
Step 1: Create image 3x3 TRANSPARENT.
Step2: Zoom in 3200%
Step3:Grab Pencil Tool, Set to 1px
Step4:Change color to black, Click on the top left corner, Now you have a small box, press in the diagonal direction (Top left to bottom right).
Step5: Make sure they're squares and they go down in a straight diagonal line.
Step6: Edit->Define Pattern->-Name Goes Here-
Now to put it on a signature
Step1: Edit Fill
Step2: There's no more steps!