Apparently, it was quite the department-store empire in Europe. Google turned up a card picturing the Brussels store:

(Image from porto-club.de via Google)
Tietz was a German, of Jewish descent. Wikipedia says that the Belgians seized the stores in Belgium during World War I as assets of the enemy, and then the Nazis seized the company, itself, after they came to power in Germany, to replace Jewish ownership with German ownership. Apparently, the family was compensated in some form after World War II.