A small 50ml pill container.
This cache is part of the Blockbuster A to Z series.
An old 80's gameshow in which contestants had to pick letters and answer questions relating to that letter to get across the board and win.
If we were doing a modern day geocache version of this I would imagine it would go:
KiwiGeoswami: "I'll have a L please Natalie247."
Natalie247: "Which L is the physical record of everyone who has signed/interacted with a geocache?"
KiwiGeoswami: "It's L....."
Natalie247: "Correct - you might want to store that away for later to see where i go with it."