I don't think there is any specific reason behind adding # hashtag which is also called pound symbol in better version of programming languages . It is that simple like we have two plus signs in C++ which is more improved version of C lang, it would not look nice if MS add two more plus signs after that. So they simply put # which is equal to ++++ four plus signs . In Programming world we use to pronounce it sharp as C-sharp , F-sharp etc . That means more evolved version of actual languages.