I use white paint markers in my work and always have one in my pocket so that's what I use my eyes are not that great anymore.
Agree on the eyes.
I've got a 20yr old pint can of paint, I just put a dab on where I start. Many of my chains I label so I can tell them apart.
My ripping chain for my Deere w/ 28" bar, .375x.050 chain is 93 links.
My ripping chain for my Stihl w/ 28" bar, .375x.050 chain is 92 links.
Getting a 93 link chain on either is easy. Wasted a bunch of time trying to get the 92 link on the Deere. Similar situation with my Efco and Stihl w/ 16" bars.
So I put a twist tie thru w/ a label and start sharpening at the label:
I pencil in the number of links, and keep the label w/ the chain, borders on ****, but with my mix of bars and chains I need something. I probably should get rid of bars of similar size requiring different links count.
Saws 'n bars:Efco MT 3600 ($50 - 10", 16"), Stihl 021 (12", 16") , JD CS 62 (, 20", 28"), Stihl 660 from ebay (28", 42")