Hi Dan,
I did this in a venue that had to comply with local law.
Device was an old Ipad running Studio6Digital and displaying the StopLight function.
Microphone was a S6D ITestMic. All up on a stand in band view.
Display goes from gray > green > yellow > red.
Lots of adjustability for meter settings - dba, leq, time, etc.
I had done a noise survey with six measurement devices around the property and a loud dj to come up with the settings.
The first wedding band in there was hitting red with just the monitors, had to really dial them back.
At the end of the evening, everybody was ok with it.
One musician said thanks, that's the most fun he's had playing in a while, and he could hear everything.
Thanks and good health, Weogo