Well, I had to ask, so I asked Officer Michelle over at the SacPD blog:
Dear Michelle, Wednesday, I was walking west on Capitol Ave. around 24 Street and I saw an RT bus traveling east with "Emergency, Call 911" on the front message sign where the route is normally displayed and "Call 911" on the back where the route number normally shows.So next time I'll know.
I watched the bus stop and let someone off and then let someone on. If it was having an emergency, it wasn’t evident.
Do the buses have "panic" buttons that trigger this sort of display?
And should I have called 911 when I saw the bus sign say "Emergency, Call 911"?
You are very observant! There are panic triggers on the busses which automatically change the front message to "Emergency, Call 911," and the RT radio control is automatically notified. You are urged to call 911 when this happens. If it is a false alarm, the driver will notify RT via radio. Way to go!