Okay, I'm the a/r vaper, lol! I want to know what's in each carto or clearo so I can refill it, and I use many flavors every day.
At first I used colored clearos: menthol in a green clearo, tobacco in red, peppermint in blue, etc. But then I had more flavors than colors, and I decided to use steel shorty cartomizers anyway. At first I used a Sharpie to write a couple of letters on the cartomizer (pb for peanut butter, tri for tribeca, etc.)
But then I began reusing my cartos for different flavors, and I switched to a code system. One carto with a dot, one with 2 dots, one with a dash, etc - and I kept a little post-it note with the codes and flavors posted to the inside of the container (eyeglass case) with all my cartos.
THEN I decided I preferred black cartos to plain metal. Metallic Sharpie marks rubbed off the black ones quickly. I tried tiny bits of masking tape, but they fall off and leave sticky spots. Finally I began using acrylic paint pens I happened to already have. Blue dot=peppermint, red line=Tribeca, yellow circle=butterscotch, etc. My code chart is still on a post it stuck to the inside of my carrying case. I keep a tiny zip bag in there for cartos I've used substantially during the day.
At the end of the day, I take out the zip bag, and check the code chart, and refill.
I know, I know, it sounds over the top....but it works great for me. I carry at least 10-15 flavors everywhere and use 10+ every day. Flavor variety is my favorite aspect of vaping, but I guess you can tell that already!