It's easier to say “don't fall” than it is to prevent the risk. I'm not sure what awareness the signs create, since you're already on the stairs. CAUTION: MORE STAIRS!
Pictures from near / outside the Sistine Chapel at the Vatican. Yes, falling down stairs is certainly NOT a good idea. First picture from a stairwell, second picture is from just outside the Chapel.
Note: the “no talking” sign didn't prevent talking, nor did the “no pictures” sign prevent photos (I was respectful and didn't take pictures inside the Chapel).