Did you know the ground gets wet when it rains?

Ok. So, when it rains in LA, it's a big deal. It doesn't happen often, so when it does, the roads are extra slippery from all the oil and stuff piling up. I get that it makes driving harder, there is more traffic, etc. That's fine. But, is it really necessary to put wet floor signs OUTSIDE? Every time it rains, there are wet floor signs outside of where I work. It's ridiculous. Are people that stupid that they don't know the ground is wet when it rains? Seriously.