Tennis balls on a walker are common. They protect floors, help the non-wheeled legs move better, etc. Rather than look like I'm 80 years old with my walker and bright green tennis balls, I bought these zebra-striped balls. I figure if people are going to stare anyway, I may as well give them something silly to look at.
I also have a pair of giraffe-printed balls as backup for when these wear out.
Oh, and Rocky is the name I've given my walker. I don't know why.