There was a time when Globe was the only detective agency in the city (or at least the only one which publicly declared its presence and its services); over the years, competing firms dropped their secrecy and put up their signboards. Somehow it seemed that there were more such signboards in Agurchand Mansion than in any other building. There must have been some advantage in nestling up with competition (easier to listen at the door when you see a prospective client walk in?), because even today, the building hast at least three firms advertising their presence - that's almost one-fifth of firms in Chennai which have the word 'Detective' in their name.
The others are scattered around the city. But who knows - they'll have their eyes and ears everywhere!