If the screen is made of uncoated glass, it won't scratch unless you use a carbide or diamond cutter, or expose it to flying sand.
Coated glass (coated with a carbide layer) will resist scratching even by carbide or diamond (it can still be cut by a diamond cutter though).
If it's plastic, just about any metal including brass will scratch it; a coating may help to resist light scratching.
Hope that helps.
Last edited by ofelas : 12-04-2008 at 09:51 AM.