I actually find that the best way to see the dirt on my displays, is to place a bright light at the edge of it.

This causes every particle and smudge on the screen to catch the light and cast a shadow across the surface of the glass.

You’d think it wouldn’t work on a transparent material, but no, it lights up every speck of dirt like the way a ray of sunlight reveals the dust that is invisible but always there, floating around mid air.