Ok, after going all eyes-crossed at the discussion about mining, here's an idea. Could we have signposts that we could stick in the ground when we don't want to be disturbed whilst doing something? I mean, it doesn't even necessarily have to be mining... leave me alone while I'm cooking, please hug me I'm low on mood, guess a number between one and eleventy to win a prize, now recruiting for bog-emptying quest, The End Is Nigh, No Really God Said So, host a barnacle party in your swamp ask me how... whatever. I don't know about everyone else, but I can't resist stopping to read notes, and if it was a deliberately placed sign, I'd definitely have to read that.
It would be like a whiteboard: write whatever you want on it, erase and re-write at will. But here's the catch: you only get one. Ever. So you've gotta keep track of it, pluck it up and take it with you, or you don't get your sign any more. It's not donate-able, or sellable, or give-able. This is your sign, you will love it because it is yours... and not leave signs cluttering up the world.
(now I'm thinking about it... we'd immediately have glitchlings lining up 4 or 5 signs ala Burma Shave. Or three for haiku. Teams could make an awesome player-created riddle/quest mechanism, or a scavenger hunt. Lo, the potential!)