I developed this system in my weave designs to code weaves. That system is a secret and I will never tell, but I can examine a piece of cloth and tell if it was woven in our plant by my secret code woven into the cloth.
I adapted it to show the size of crochet needles. Here a bead equals three and a ring eguals one. So, the 10mm size has 3 beads and 1 ring.
The 5mm size has 1 bead and 2 rings.
When we were doing the light sabres I would ask the kids their age and we would make a small cove for 5 and a line for 1.
Lots of things can be marked this way.
What have you done to mark a date or size besides just stamping or wood burning the number?