Both of these can be accomplished by using map metadata. You should keep a 2D array which represents the special data in the map, then when the character performs an action, you check the corresponding data in the array to see what you actually need to do.
For instance, if you have a map drawn out already on the BG and the character presses A, you could check the map using something like BGGET to see if the BG tile in front of you is a sign, then you could check the metadata array at the same position to know which text should print.
None of this is going to make sense unless you have a decent grasp of programming though, so I would definitely suggest looking up tutorials and starting MUCH smaller than an RPG if you're just starting out. An RPG is quite difficult to make.