Not all blue tapes are alike. The Scotch 2090 that seems to be more common in hardware stores has a crepe backing that will leave impressions in a fresh finish, and it also leaves adhesive residue. Scotch 2080 (not that hard to find; paint stores usually have it) has a flatter backing, leaves less residue, and is safe for longer times. But it's still a good idea to dull the tack by sticking to your shirt first, and get it off the guitar as soon as possible (couple days max). You may need to buff a bit to restore the surface. 2080 is what I use.
The green Scotch is supposed to be the most safe for lacquer (nothing in its adhesive is a solvent for lacquer, unlike the others), but it also has a very high tack. I haven't tried it yet. There is also a yellow low tack Scotch, but it's hard to find and I don't know if it's lacquer safe. I know you used Tru-Oil, but I don't know which solvents will attack a cured tru-oil finish.
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Howard Klepper
http://www.klepperguitars.comWhen all else fails, clean the shop.