Placards and bullhorns are used to express positions. Picketers with bullhorns identified picket-line crossers by name. He made demands to represent himself, dressed in pajamas, shouted through bullhorns, and rambled incoherently. "Revenge for Eisner" rang through bullhorns in the streets. New York City requires a permit to use "amplified sound", including electric bullhorns. A principal weakness of common speaker systems and bullhorns are their clarity.