Whether you want to keep track of a bunch of stuff or tell people who made it, there isn’t much simpler than using a number and letter stamping set. These hardened steel stamps can be used on wood and softer metals like brass and aluminum.
You probably want a 36-piece set, which usually has stamps for A through Z, 0 through 8 (9 is 6 upside down), and an ampersand. The stamps sets come in several different character sizes such as 1/8″, 1/4″, or 3/8″.
The 36 piece 1/4″ letter and number stamping set from Harbor Freight will run you $11, while online similar sets will run you $25 or more.