When did you first notice green flashing beacons atop construction equipment?

I thought maybe they’d started appearing about a year ago, apparently in the same way that I think Pop-Tarts are a newfangled breakfast phenomenon. But I’m wrong, because they’ve been around for years. 

If you read Highways England’s publication ‘The Delivery Hub: health, safety and environment – raising the bar 1’ (and I have so you don’t have to), the green beacon is mentioned no fewer than 12 times as being best practice on construction vehicles. It was published in 2013. (Six years ago! Surely, this isn’t possible. If you’re a constructor, please tell me you’ve only started fitting green beacons in the past fortnight.) 

What does the light mean? That somebody on board is first aid trained, given that green lights are the preserve of doctors on highways? No, it signals that the operator is wearing their seatbelt.