I've been doing this for a while now and it really works great. I have too many reels to keep track of what size/type line I have... hard to tell the difference between 17 and 20 lb in some cases, also I have some brand specific spooling that I need to keep track of.
I use our p-touch label maker that has the 6mm tape in it, which works perfectly on the area for a shimano reel I use. The sticker stays put, doesn't wear off, and removes easily if I change up the line. I typically use the pound test followed by the brand or model ie; 25ABRAZX (25# Abrazix Flouro). If you reduce the font size down, you could probably put a date stamp on it as well.
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