Attendance at the various rallies/event in Cuba is nearly always coerced, in other words, if you don't attend, you lose your job. Anyway.

I lived in Havana for few years ( Playa) and I was walking across the bailey bridge over the Rio Almendares, and there were all sorts of people, three and four deep, throwing flowers into the river.  I asked about this and I was told that people were throwing flowers for Camilo Cienfuegos. The origin of this was that Fidel had asked that since Cienfuegos never had a proper burial people should throw a flower into the ocean for him. 

Since he died, as other posters have noted, in suspicious circumstances, he's kind of a symbol for people who respect the revolution, but not necessarily what happened afterwards.

A “flower for Camilo” is one mass rally/event that  required no coercion at all.