It is a rotator, one of the few still being made I suppose. It's a Cat Series 394 made for Caterpillar. Nice light that came NIB for a good price so I thought I would add it to the collection. Nice, very bright light with magnetic mount.
@Skulldigger
Britax is an old manufacturer of warning lights in England.
They are a part of Ecco Safety Group as Code 3, Delta Design, Hazard Systems, Nova Electronics, Premier Hazard and Vision Alert to name some of the companies.