I'll nod at people I pass on a bike
And about 95% of the time they nod back.
What was cool, or I thought it was anyway, on the second day of STP this year there was a motorcycle in a turn lane and I happened to catch his eye. I smiled and nodded and he nodded back & gave a thumbs up, then went along his way. I've seen motorcyclists nod and wave at each other, but don't think I've seen one respond to a bicyclists. (And no, it was not one of the Gold Wing people this guy was on a Harley and decked out in leathers).