Hey Skid never be embarrassed this forum is so useful that I'm sure even pros learn many things on a weekly basis! As mentioned already, Nikkor lenses DX ED-IF lenses for digital bodies only will always be marked in "DX" paint. Generally these lenses are not very old. FX glass is the Nikkor D Type AF lenses.
This being said, third party manufacturers can throw you some curveballs so things can get tricky. Tokina only produces DX models right now as far as I know. 35 macro, 10-17, 11-16, 12-24, another 12-24 Pro II, 16-50 and a 50-135mm. I hear they are working on FX glass though. Tamron lenses must say DI on them so they can be used for film bodies or digital. The Di II lenses are their DX lenses. Sigma DX lenses are marked DC and their DG Sigma lenses are for full frame (film or FX) bodies.