I wrote the word "FUCK" on a big piece of paper because it expressed how I felt about the death of Freddie Gray. I'm white and I'm aware that I benefit tremendously from the problems we were protesting, so I feel guilty for grabbing so much attention at a rally that I was supposed to be supporting, not coopting.
As a person who suffers from Tourette syndrome, however, there might be nothing more cathartic than broadcasting the word "FUCK" to tens of thousands of people. I'm not being facetious about this. Most of my tics are physically painful and unsatisfying, but the words are a little better. Phrases like "fuck" and "I'm gay" are some of my least unpleasant tics, even when I'm just sending them to friends of mine in text messages. (Edit: This is called coprographia.)
I also figured that the risk of it getting media attention was low because conventional news media would have trouble publishing it, and it's true that it didn't make it into any actual publications, as far as I know. One thing I want to avoid more than almost anything when I go to DC Ferguson actions is being prominently featured in a photograph in a major publication and becoming a symbol of narcissistic white yuppies going to Black Lives Matter protests and treating them like pep rallies.
Regardless, I don't think I'll make any more signs when I go to DC Ferguson rallies in the future.