Not sure, but I don't think it JUST means a 'flashing light' — I've only ever come across 'flash' in FR used in terms of a photographic flash unit. I suspect these are in fact the kind of xenon flashing beacons that actually have a lot in common with an electronic flash unit. They are very commonly used as reliable warning devices, since there are no mechanical parts to wear out, and the intense flashing light is hard to miss.

As for 'report', I suspect this is being used in the properly French sense of 'carried somewhere else' — i.e. a beacon that is located away from the actual central control unit; traditionally, this would be on the street frontage of the shop premises, for example.