Im from the UK. One day (in the 1980's) we were all given forms that we had to sign and send in to get our little MAC cards. I dont know why. I dont know if it is current practise still.
In the UK, if you were on the black belt-register, theoretically you could be more likely to be held to be an offensive weapon rather than just brawling. Not that I ever did that, but I didn't like the idea that one day I could be defending myself, the next moment finding myself being prosecuted for attempted murder just because I punched some lowlife into hospital
[1]
A..
[1] This characterizes the way I used to think - not how I think/behave today. I did eventually grow-up.... a bit.