I marked my Tretorn pressureless ones as well with a Sharpie but for hitting sessions, I just use the two tone Penn Radical balls which is very obvious who owns them .
I do mark my tennis balls with a Sharpie. I came up with a logo and I remark them every month.
Where I teach, there is another pro who is giving instructions frequently on the adjacent court at the same time as me. Sometimes I run into other pros too. Some do the dot thing so I decided to have something that really lets them and their students know when one of my balls gets to their court.
I am repressurizing my tennis balls also, so remarking them is essential.
I use a red Sharpie, and follow the seam (the rubber part of the ball, not the fuzz). The red lines created this way last longer than 1 year. I used to draw crosses on the fuzz, but it takes too long. You have to hold the sharpie a few seconds, to let the ink sink to the bottom of the felt.
I name my Tennis balls. It lightens the atmosphere and gets people talking. Right now I am hitting Charlie Sheen, Lady Gaga, and Jose'. It's a little different.
I label each 600+ balls a unique name. My border collie keeps track of each
ball. I just call the name and he brings the correct ball.
http://abcnews.go.com/Technology/wo...special-shows-border-collie/story?id=12875750