I just ordered engraved pet tags for my does and doelings. I'll get the boys next time around. My little girls like to wander a bit, and aside from that, when I have an occasional "guest milker" (rare!) they will be easy to identify.
The best deal I have found is on Etsy, Jeffrey's Pet Tags
These are extremely reasonable. I found so many really cute boutique type tags, but let's face it, the goats need something that won't wear off with barn life. The tags I found are plain and sturdy and engraved, not plastic with ink, like the really cute ones.