I'm sometimes out for a long time, making photos while hiking or visiting friends. I have no sharpie in the wild. What I have though, is my terrible memory. I reload all cassettes many times, with different films, so the info on the cassette is insignificant (so is DX code, so I'm sometimes taping these, depending on a camera). I'm always leaving the beginning (it's hard to call it a leader) of a film sticking out when rewinding the film for more confusion. Helps reusing cassettes.
So you can imagine this situation: smelly guy, tired as hell, working in a hurry in the middle of nowhere, cause the sun is going down... With a bag of films, all looking the same. That, without a clear and working solution, would lead to a complete chaos followed by a certain failure.
There's a system that works for me. I'm scratching whatever I'll need in the emulsion with whatever I have in my hand. Pen, knife, cable release, pebble, whatever. If I'm in a real hurry, I'd bite the film to mark and remember which roll needs to be taken care of later and should not be used. I scribble a place I'm in, the number of a roll from a given place and push/pull info if needed. After getting back home, I have have zero problems with developing, chronology or subjects, and the information isn't lost even after the development. S2 50 translates to: sea, second roll, 50 ASA. I may (or not) remember which rolls or subjects need more or less contrast while developing, so I can process things accordingly.