I thought those were so off-duty firefighters are able to respond to calls as-needed, no? They usually have their personal vehicles outfitted with those blue l

I thought those were so off-duty firefighters are able to respond to calls as-needed, no? They usually have their personal vehicles outfitted with those blue lights and the plates make it easy for any officers coming up behind them to see that they are legit and didn't just buy the light on eBay so that they could speed or do whatever on the road. I could be wrong, but I am reasonably sure that's what those are for.