State Police and the state Department of Transportation are using electronic signboards to get people with ear buds to take one out  - so they can hear that ambulance coming up behind them and not risk getting a ticket:
The use of only one earpiece is acceptable under current Massachusetts law. Frankly, there is no legitimate reason for an operator to be wearing both headphones while driving. The campaign is to inform the public that wearing both headphones or “ear buds” is unnecessary and unlawful. This is a primary offense allowing police to stop and cite motorists when they’re observed to be wearing both pieces in their ears while operating a motor vehicle.