In the season 3 episode titled "Rains of Castamere", the band at the wedding starts to play a song that worries one of the guests. I later found out that the song was "The Rains of Castamere" - the Lannisters' "song".
Without having read the books, how would I have known that the song being played was of any significance at the wedding?
Further, how would those who HAVE read the books know what the songs sound like - especially since even if they knew the lyrics to the song, it was only orchestrated at the wedding without any words being sang.
This question can be applied to all of the songs including but not limited to the Starks, Greyjoys, etc..