MIG wrote:
I would take "ambulance" to mean a vehicle which carries sick or
injured people.

The word "ambulance" on this vehicle more likely relates to the fact
that it belongs to the ambulance service, just as it would if it was
written on a bicycle or a building. (And such buildings or bicycles
would need to be treated with appropriate respect, and not
obstructed.)

If a vehicle falls under the legal definition that allows it to bear the
designation "Ambulance" and does so, then it is legally an ambulance
and entitled to various legal privileges that don't apply to ordinary
vehicles.

Years ago, my father, then a London bus driver, used to be a volunteer
ambulance driver for a disabled ex-servicemen's charity. The ambulance
was a Bedford coach converted to carry wheelchairs but it was legally an
ambulance and bore the designation. Sometimes if he was doing a trip
that started early, he'd collect the ambulance the night before from the
bus garage where it was stored and park it outside our house. Some
neighbours complained to the council that we were parking a bus on the
street so the council put up a "Buses prohibited" sign outside our
house. The next time my father parked the ambulance outside the council
threatened to prosecute. We pointed out that the vehicle was legally an
ambulance, bore the designation "Ambulance" and therefore could be
parked on the street and we never heard any more about it.

My understanding is that "Ambulance" is a protected designation and it's
an offence to apply it to a vehicle that doesn't meet the definition.

--
Roy