Because it refers to a certain year overlapping or two years on the trot.
It could be someone's initials.
I have been awarded prizes and they gave me a choice of Cap or Tie from the Gents Outfitters or a Book.
They give you Vouchers, but I like books, but the Cap or Tie was to be embroidered with your initials.
Anyone in your family (or the family that the Cap belonged to) with those three initials?
My Grandmother won a Scholarship to Grammar School c.1920 and her initials are printed on her School Case we have.
Mark