From their event page: 

An invitation to all cyclists for the 21st Philadelphia Ride of Silence. For the past 20 years, cyclists throughout Greater Philadelphia have come together to ride silently in honor of riders killed or injured by motorists. Although bicyclists have a legal right to share the road with motorists, the public often isn’t aware of these rights, and sometimes not aware of cyclists themselves. The goal of this annual, international event is to not have another ride, but to have a year with zero bicyclist deaths.

RSVP for ride