How To Trigger a Switcher using SRT

I have two sites and I am sending an SRT stream from site A to site B where there is TV broadcast equipment. At both sites, I have Pearl Nanos. At site B they want a message board to play when site A is not “On Air”. Is there a way for the Nano to output no video when the SRT stream ends? Currently, the Nano outputs a “No Signal” image. This would allow for an HDMI switcher to auto-switch when the SRT stream stops.
Or is there a way to get some sort of triggering signal out from the Pearl Nano that a control system would sense and trigger the HDMI switcher?