Please Explain:  Sheep on Broome Street

You guys were great at explaining the Bertrand Russell graffiti mystery over the weekend, so now we've found another puzzler for you to unravel. We've seen a bunch of these sheep all over town these last few weeks-- but this one carries the puzzling message "stop the sheep-- fukc the shepard." Who are the sheep, and why do they need to be stopped? And who is this shepard? And why does he need to be fcuked? We are seriously confused.