I've googled around a bit. Hantak was a gentlemen's outfitter and tailor in Vienna, located in the city center (first district = Wien 1), on Opernring 15. This is a very prestigious address, near the art museums like the Albertina, the Opera itself and Karlsplatz. I didn't find any history or from when until when they were in operation, but there was an article talking about someone having found a made to measure suit at a charity shop that once belonged to Austria's then-president Bruno Kreisky, which had been made by Hantak in 1975. So it looks like Hantak was something like an official retailer for Burberrys at some time.