What are less obvious signs to you that someone is intelligent?

The khaki pocket one and the funky, offbeat clothing ones aside, I don't these are dumb. I particularly agree wtih 2 (shows the person is open-minded), 3 (a respect for language by using correct grammar is rare these days), 6 & 7 (again show an open mind). I would add to these having a sense of humor where the punchline is not always obvious, for example, dry or satirical humor.