"Surface may be slippery in wet weather"
We're talking about stairs here people. Stairs that may be slippery in wet weather. You know what happens when stairs get slippery? Cancer! And Explosions! So have caution around stairs that are wet and slippery or you might get cancer and explode!
This was a public service announcement.
I'm no physicist, but I'm pretty sure people after the age of 12 know that wet things are generally slippery.