Since Mn doesnt require a portable license any more and I dont leave it unattended or overnite I used a permanent marker on the inside with ownership details ,big enuff to see but small enuff to blank out if sold.
I have the plastic holder that dandorn mentioned on the front of my Voyager. Just wrote my DNR# on a piece of cardboard with a black marker and stuck it in the plastic. Works great and that way you don’t have marker or paint all over the house itself.