I couldn't find anything showing people singing apart from these two PHQ stamp cards, and that only after hearing someone bemoaning the fact that they had just heard their first Christmas songs.
The top shows 16th century carollers singing the Boar's Head carol, a Yuletide tradition that may date from much earlier. It continues on today in the form of the Christmas ham.
The second shows a band of musicians known as a waits or waites. They were traditionally a band of pipers employed by a town or city.
There was originally a set of four in the series, "Joyous Carols of Christmas", designed by artist Faith Jaques. Her original art features on the First Day covers.
This is a post for Sunday Stamps, now hosted by Violet Sky at "See it on a Postcard!"