Hey,
I had a play with QR codes and generators awhile back.
I also made some prototype ones using HAMA beads (heat melt plastic beads, arranged using a peg board, a kids toy in the UK)
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Found encoding anything large in them to be cumbersome, but maybe worth thinking about as the end results are tough, waterproof and if you epoxied a dog tag to the back would probably serve quite well.
- Alex