So is it writable or something? Can I like, write my npub to it or something and someone can tag it and get my profile?
Discussion
Yes they have like 800 kb of memory and you can write anything on it if it fits. In bitcoin they are used for lightning transactions. Of course you could put an npub or any other link and read it with a smartphone. For example I have one that brings you to my Nostree page when you tag it.