I guess my system is complicated but here goes.

I tag the tubs with a keyring thats hold a tag. The keyring states either male or female and then a number/letter combo like this.

F01NOR

This means Female, first one I've bought, and normal genetics.
You can cross ref that to my log book and see when the animal was born, weight, eatting schedule, etc.

M35SPI

Would mean Male, 35th bought and Spider genetics.

Etc. Mainly use what works best for you.