I did the same thing a while back.
I made sure that my instructional signs were bilingual.
After 32 years in the business I posted for the first time caution signs about the floor may be slippery or icy when wet and high pressure guns, use at there own risk.
Also that the bubble brushes do not work in freezing weather.
I had a guy recently that complained to me that he wanted all his money back($5) because the bubble brush didn't work, the temp. was 12 degrees the wind chill was below zero. I looked at his car and it was clean with ice all over it. I showed him the sign and he started laughing and said it probably wasn't a good idea to be washing his car when it was that cold.
He was at the car wash last weekend (27 degerees) using the brush.
There are just times when my brushes will freeze no matter what I do and invariably a customer will try using them when it's frozen with ice cicles hanging from them.
With the economy the way it is I am worried that some people might try to get a fast buck too.