The crest above the entrance says "k crnom orlu" which means something like "at black eagle's". This eagle, I'm guessing, might be some left-over from Austrian-Hungarian monarchy. Right below is the official (but old) crest of Zagreb. I'll leave its explanation for some other time.
FYI, the oldest pharmacy in Croatia is in Dubrovnik (dating from beginning of 14th), and it's the 3rd oldest pharmacy in Europe.