This is probably a pretty dumb question, but I didn't find anything relevant using the FAQ or search, so:

Is it possible to create new powerups (like the double jump, etc.)?  I had the idea of turning the player's ability to jump into an item, but I have no idea if the editor supports this.  I'm guessing the answer is probably "no," but I thought I'd check anyway.

On an unrelated note, where is the sign tile used in the KS tutorial?  I'm still pretty new to this editor and I haven't found it yet. >_<