I use the spaces between my teeth if I can't remember. If that does not work I use my tounge. If that does not work I go home.

use a label maker like one of these

http://www.officedepot.com/a/products/571842/LetraTag-Plus-Handheld-Label-Maker/

me and my dad are pretty basic 20ld on t rig, 12lb on crankbait, and 20lb on spinnerbait. thats all we use is 20 lb adn 15 lb on everything

I use colored "dots" from the office supply store. They come in numerous colors and I keep them in the line box and a couple on the outside of the line box for id purposes. They are smaller in diameter than a pencil eraser so they don't look bad on the side of a reel and they don't leave the adhesive junk when you peel them off like tape does. For example I use red dots for 12lb test, green for my sixteen lb test, yellow for 20 etc. They come in rolls of 100 I believe for less than $1.00 so they last years. Easy, cheap and not messy on my reels. Spool the line on and stick a dot on the reel, simple as that.

I only use 17 and 20 lb depending on the setup on each rod. Pretty easy to tell what line is on each reel.

Mine is a little more work but very accurate...I cut out a piece of paper approx. 1/3" x 3" long, then write down the line, size, type and date I just put on reel...i.e. (#10 Seguar fluoro 8-28-08), then scotch tape over the top of the writing, then tape it around the butt end of the rod. I can just glance down when I am fighting a fish to see if I can horse him in or have to finesse him in. AND it is very waterproof and lasts a long time! (Actually too long, because it reminds me that the line has been on there too long and needs changing!)

On spinning reels I use a label maker in small print and stick it inside the reel. On casting reels I use the same label maker and stick it to the bottom of the reel foot.

I take a small piece of masking tape, write the # test and 2 or 3 letters identifying the brand and place it on the bottom of the reel seat. It is completely hidden, but how ofton do I need to refer to it? I also keep a note in the boat/tackle box telling me what line is on what reel/rod.

Cool.. another handy use for my labelmaker. SAM's has them cheap.

I use medical tape placed under the foot of the reel. All you have to do is to loosen the screw on the reel seat and look at the underside of the reel foot. This placement seems to protect the tape and writing.

TFP