Those look so rad. Huge respect to the person /people who put the work into making those. Makes me wish I had more 3d printing/fabrication knowledge…

Hmm interesting problem. A tiny dot of colourful non-toxic paint is what I would try. I did a quick net search and the results I found all mentioned an electronic tag with invasive insertion procedure. If only a tiny belt would stay on…

Might be worth checking out cryptpad.org. Open source, encrypted online productivity suite.