Cajonjp sorry I don't have any pics right now of the the wheel markings. But at knotts we just spray white paint on the rims of the wheels. I spray a mark about 12" long.
About a year or so ago I noticed that someone had marked the wheels a long time ago, with yellow paint(you could hardly tell there was a mark). I asked if I could do it again and got the ok. So I went to it with a scraper, some degreaser, and paint. Its nice to be able to look back and see all the wheels rolling. Iv only had one guest ask what its for.
The other guys are right though, it only last's a few weeks then they get covered in oil and grease. In fact its time for me to do them again.
Also some journals leak more than others, so sometimes on the same truck one axle will get so dirty you can't see the mark and the other is still visible.