They didn't seem to be required until the mid-'80s. Optional before. M-M even used some fender-mounted Ful-Vus for this purpose.My 1978 Superior Cadillac ambulance doesn't have them, so I doubt that they were a requirement then. Possibly today they are a requirement.
These are indeed red flashing light better known as intersection lights. They were and option for many years until they became required in the Federal specs which you will see them on ALL later model ambulances.