I like the Element concept.

Carbon could be construed as a hint that you might have some carbon fiber... or you're a misguided ricer.

Aluminum? Who are you trying to fool? (Plastic, we'd believe)

How about something radioactive like Uranium? Or light like Helium? Or that can create bright light like Xenon?

The most honest choice would be Iron or FE. "FE IRON" would get the point across.

Or... "PB LEAD"