If you check my tool kits, you will always find Sharpie marking pens. Why? Because there are several markings that can make a big difference.
1.) Name: this one is obvious... but sometimes kids pickup similar looking skis. My son tried to step into another racer's skis one day- but fortunately the skis had the other kid's name on them.
2.) L/H and R/H. Why mark left and right? Because the boots wear and the binding fit may be different. Also, the edges do not wear evenly and by determining which ski is which (rather than let chance decide), you can decide which is the better edge to be used as the inside edge. There are many more reasons, write me if you need to know more.
3.)Tuning and binding settings. Skis may get handed to a shop (or friend) to work on. If the usual settings are clearly marked on the skis, it reduces confusion and improves quality.
4.) Day Counter: simple hash marks for each day used. I started doing this many years ago, and I find it very useful for tracking wear and predicting performance. Skis only last so long, and when you track useage, you can figure out how long they last for you (or your racer).
5.) Blackening Edges: There are purposes for blackened edges:confirming a bevel angle, testing a new tool, to help a tuner develop "touch" etc. I will add pictures to better illustrate.