You should definetely use QR Codes if you want to print it on paper. I think a "secure enough" ID would be really a hassle to insert into your browser just with

You should definetely use QR Codes if you want to print it on paper. I think a "secure enough" ID would be really a hassle to insert into your browser just with your fingers. Or you sell small USB sticks with just enough flash to store your link on it (in which case increasing the minimum to 10€ would make sense). Or maybe I'm just too simple minded and you have some creative ideas to make your IDs secure and handwritable for my Grandma?