Трир — Родина Карла Маркса

This should be trolleybus 4 (plate number FR 53-7015).

I think under the city coat of arms on the right side of the trolleybus I can also read the fleet number "4".

By the way the license plate is an occupation license plate (Besatzungskennzeichen), which was in use in West-Germany until 1956.

And the location should be Porta-Nigra Platz. The building to the right was demolished in 1967 and replaced by the ugly one: https://www.tch-hotels.de/media/portal/i...bf2.jpg

Note that the tram tracks are without an overhead line: trolleybus has replaced the tram route here.
The picture was likely taken in the early 1950'ies.

See also: https://pictures.abebooks.com/inventory/30365726616.jpg