“The L.A. City Council last December passed a new ordinance that effectively banned anyone but local artists from engaging in commercial activity on the boardwalk’s beach-facing side. Ordinance violators are subject to fines and repeat offenders can end up in jail. That has left it to officers like Sgt. Gonzalez to routinely weigh in on a debate more suited to the Museum of Modern Art or the Guggenheim: What constitutes art?”