If you have one rod, one reel, and one fly line, you pretty much know your equipment. But few Nor'east Saltwater fly rodders have such limited arsenals these days, and things can often get a little confusing when you're rummaging through your gear.
Rods and reels are easy to keep track of. Fly lines are something else again.

Those little line-weight stick-ums that come with lines usually don't stick very well, and they're of little help unless each is matched to a line that's always at home on its own spool. Add a full selection of Shooting Head sink rates to the mix, and reaching quickly for just the right fly line can turn into quite a problem.

Fly rodders have come up with a variety of ways to mark fly lines. Lefty Kreh suggested coding the line with a permanent ink marker, so several seasons ago, I came up with a color-coding method that seemed to work well with braided monofilament loop connectors.
Like most monofilament, the braided variety is absorbent, so it sucks up and holds the various ink colors. Back then, it was fairly easy to remember that a blue ink loop was a 10-Weight Type 2 Sink, green was an 10-Weight Intermediate, etc. In fact, it was fairly easy to remember which line was which just by looking at the line itself. There was no mistaking the light green Intermediate Shooting Head for the dark green Type 2 sink.

But I discovered that permanent inks weren't so permanent when they were doused repeatedly in salt water. And as my tackle grew, my brain cells were taxed, keeping track of all of those colors.
Looking at the lines themselves didn't help. I now had several light green Intermediate heads in various line weights, and several different sinking shooting heads to balance with several different rods, not to mention three Deep Water Express heads that all looked pretty much alike. Sun and surf was also beginning to leave their marks on my little color-codes. Was that red or pink? Obviously, the color-code system was falling apart.

I needed a new system, one that simple to remember, and permanent.
I started with a narrow band of dark blue ink on the stem of the butt loop connector attached to a line or head. It made sense to mark only the butt loop because we store our lines This End To Reel out. Then I realized that things I also needed to know what line I had on a reel, so I began marking both butt and tip loop connectors.
The blue band is my Base 10, standing for 10-Weight. Working from the end of the line, a blue dot to the left of the band designates a 9-Weight, two dots equal 8-Weight, etc. Dots to the right add a line weight.

Now what about sink rates? Switch colors. Intermediate was now my base, and required no mark. I used a red marker to add bands for #1 through #6 sink rates. Whatever colors you use, make them different enough so that they'll stand out under the light of flashlight at night.

To make sure those reference marks stayed put this time, I give them a very light coat of Softex. The stuff is durable and the marks will probably be there for the life of the line.

If you have a fine-point pen, and a fine hand, you can use a Roman numeral system, or any system that triggers your memory. The real key is the rubbery, flexible Softex that is able to protect the codes without putting a stiff spot in the line, and without damaging the line's coating.