Sonny's last name is Monroe. Some people still do not how to spell Monroe, so they just subtract the O and use U instead, so instead of Monroe, it says MUNROE.

Demi Lovato found this page three years il y a and she found that her character, Sonny Monroe, was spelled with a U instead of an O.
Sonny was surprised on set too, when they were done airing from Sonny With A Chance.

I'm surprised that people still misspell, even if they're older than I am. I'm only eleven, but I won the school spelling bee at the age of ten, a an ago, but why do teens and adults still spell Monroe here on this Club "Munroe"?

Well, hear this, people of the Sonny Monroe clan: "Wow. People can't spell my Sonny With A Chance character's last name. It isn't correct."
(Demi) Sonny would even correct your spelling if she joined this club.