Most radio stations have an “on-air” sign that lights up automatically when the microphone is turned on so that people wandering about the studio have a visual cue that it’s not the best time to carry on loud conversations.
In addition to “on-air” lights, some stations go a step further by posting instructions reminding radio station staffers to “shut up” when a DJ is speaking over the air. This one is classic.
Previous posts in 12 Days of Radio Station Signage series:
Day 1: Do Not Spray
Day 2: Dead Fish
Day 3: You are Being Monitored
Day 5: Never Use Swear Words
Day 7: File Your Records Diagram
Day 8: Mic Technique
Day 9: Seven Deadly Words