On diamond and pearl (where unkown are), I've been wondering because I think they say somthing but I can't figure it out.
Each Unown represents a letter, and the signs are made of unown symbols. It can be a bit difficult but you can ork out what each sign says.
The first one gives you instructions on which rooms to go into, that will take you to the main room at the bottom of the ruins. It reads:
all lives meet other lives to make somthing a new and alive friendship
the one at the end of the tunnel spells MYSTERYSHOCK (? and !)
there is a fouth code: friend