This looks awesome!
In case the lettering isn't legible, here's what it says:
Midnight Bike Ride
Meet at Robin's Park / Off Fifth St + Park Ave / at MIDNIGHT!
I like the picture. Somebody told me these people are of many different ages, and there're actually quite a few of 'em! Someone overheard our conversation, and was excited to hear the explanation for this massive posse of silent bikeriders who took over the road as he was driving late one night.
(Bike ride organizers, feel free to contact me if you would like your poster removed from the site)