OK, here's a simple tutorials on how to make diagonal scan lines in Photoshop CS. Ok, lets begin.
Creating the PatternStep 1:
Open up Photoshop CS and create a new 3x3 pixel image.

Step 2:
Zoom in as much as possible. It should look like this:

Step 3:
Select the pencil tool and adjust the settings to these:

Step 4:
Now with the pencil tool, fill in the bottom left, center, and top right areas. It should look like this:

Step 5:
Now, go to Edit -> Define Pattern. Now name your pattern (I recommend something like "Diag. Scan line" ) and click OK.
Applying the PatternStep 6:
Now to apply the scan lines, open up the image that you would like to use, I will use one of my sigs.

Step 7:
Now, create a new layer and go to Edit -> Fill. Now pick the pattern you just made and click OK.

Step 8:
Now, your image should look something like this:

Step 9:
Now change the opacity to about 25% and it should look like this: