If I bother labelling them at all -- and I usually dont, with my ADV strawberry & cream, but with other flavors, I might -- I use "removable" labels that I got at the officemax, and write on them with pencil -- same way I label my nicotine for freezer storage -- because PG will make ANY ink run and ultimately vanish, but leaves pencil-on-paper almost completely untouched, so it stays readable.
The "removable" labels sometimes don't stick well, and I just add a piece of tape, over whatever I wrote on the label. Either way (the label and/or the tape), it doesn't leave a sticky mess when removed.
Also, with Inawera flavors, their labels are metallic mylar, so if you peel them carefully off whatever bottle the flavor came in, you can re-use those labels on glass bottles -- which is exactly what I do with my shisha strawberry -- the 100ml bottles used to ship in glass, but now in plastic, so that explains the lower shipping cost, but I can't leave that flavor in plastic, it might melt it if left too long.
Andria