I have a roll of the 1/4" quilters masking tape in my tool box. Mostly because of vision issues, I'll often use this to mark my cutting lines on my rulers. While it is really fast and easy to put put on the top of the ruler, if you put it on the bottom, it also helps provide a little traction which can really be nice for trimming small pieces.
Is also cheap and easily removable/reposition
This shot just shows my trim line on my little 2.5" trimming ruler, I can't read the markings at all but I can see my tape!