If you go to Home Depot, in the paint department is a section devoted to Disney color paints. If you look, some of them are Mickey Heads in the individual colors. Most of us use the Alien Green Mickey Head. Some laminate them as is. Some put their DISname before laminating and some don't bother to laminate. (They have the sticky kind that doesn't need heat)
We put them on backpacks/purses/diaperbags/camera straps. Put them on hotel doors. Make our kids wear them on their hats. Just kidding about that one.
It is a way for DISers to recognize fellow DISers. You are not obligated to stop everyone who has one. And you don't have to take up much time if someone stops you.
It's just fun.