I wore nail polish quite a few times before transition. When I did, the people at work downstairs (who didn't know beforehand) weren't that suprised. Apparently, to them, the nail polish was a dead giveaway (except to one girl who assumed I was a goth), but they just talked amongst themselves and assumed it was a 'hobby'. Yes, they really did call it a hobby.
Just my observations, for what it's worth, that people 'think' things even though they don't say them to you.