thanks so much for your feedback. i'll try to make these things more intuitive over the next few releases. in the mean time, i'll try to clarify:
the keys are a partially implemented feature- they will be a multifunction key / collectible in the next release.
there's currently a bug which can cause tiles to be solid (or nonsolid) which shouldn't be by default. i'm working on a fix, but in the mean time, should this happen, you can fix tile solidity by holding the shift key and clicking.
you're correct- signs aren't implemented yet (but will be in v. 1, later this week!)
(your game is coming along nicely, by the way)