It's called a stencil. Sometimes it's just the frame logo, sometimes it's the frame logo combined the string logo depending on endorsement contracts.
I stencil my racquets but be aware that it can be a pain in the *ss depending on the string. Luxilon strings for instance don't absorb the paint so you have to do it every match or so.
I used to do my Babolats all the time, then when I got my Wilson's I kinda gave up. Now I try to put the luxilon logo on my 6.1's whenever I remember. I use gosen strings though, poly mains, syn crosses, so it sticks to the crosses, but not to the mains. Looks really cool though