1000 refers to the "Little Night Music" song "Send in the Clowns". 1001 refers to the "Sound of Music" song "Maria"...
A page from comic artist Lee Sullivan A frequent in-joke included in city backgrounds drawn by Sullivan is a 'MacKays Music' sign or store front, a reference to Andy Mackay, the saxophone/oboe player of the UK group Roxy Music, one of the saxophone-playing artist's heroes.