For a while there was a contest called Hunt and Find. I noticed it hasn't been active for a while, so I thought I'd start one of my own. It will work much in the same way. I hid a sign in the mining world. If you find it, take a selfie with it and jot down the coordinates. Than message those to things to me on the forums and I will give you instructions on how to find the treasure chest. The chest is a locked chest not in the mining world, and currently contains 8 diamond blocks, 5 nstars and 30 iron ore. If know one finds the sign before the mining world is reset, I will add a little extra to the chest and put out a new mining world sign.
The sign is on the surface of the mining world.