It's from street projects. Being a top contributor got you trophy pieces which then assembled into a whole trophy. There was rock, dirt, earth and wood.
I knew about rock, dirt, and earth, but not wood ( I was able to get one peice of rock before street projects stopped :/). All this imagination commotion's got my mind in a tizzy :p
Hi Muncey--those are trophies that can be achieved through coming in as one of the top 3 contributors to a street project (you have to do this multiple times; each time you come in the top 3, you get a trophy piece). You need to collect all 5 pieces of each trophy to assemble it. As Nuh' says, there are several different ones.
We're not sure what's happening with street projects or whether it will be possible to still achieve these trophies.