The title is a play on the old nursery rhyme "Sing a Song of Sixpence" which has the line "four-and-twenty blackbirds baked in a pie". The rhyming scheme is kind of similar to it! I'm not sure how that happened...hmm
Anyway the actual "Sing a Song of Sixpence" has been interpreted in lots of different ways. Most of these old nursery rhymes often have more significance than it seems.