Does anyone recognise this Zurich stamp in a '70s warranty book?

I'm trying to identify the "H. CLASS" stamp in a 1972 Eterna warranty booklet. It doesn't look like the name of a Zurich watch retailer and my internet search drew a blank. It might be a Swiss customs / export / tax stamp? 8004 is the postcode of the district that borders the Hauptbahnhof and the main Post Office is there. The major watch retailing area is outside of 8004 in the neighbouring postcode. Do any of our Swiss or other members recognise it?

Brilliant find! Indeed there still is a watch shop under a different name at that address. Thank you Tony.