Thermo signs

In London this week I was puzzled by this sign which told me, "If the word "Warning" appears above, there is a possible risk of slip conditions"
I looked above the sign to the high walls of the multi-storey car park but there was no word of warning. My friend then walked up to the sign and threw water at it, which shocked me as she is a very mild mannered woman not given to angry outbursts.
It took me some moments to register that this thermosign is a thermo sign. I had no idea there was such a thing. My friend's water was not sufficiently chilled to fool the sign into revealing a warning. I am still confused as to why if it is cold enough for ice to form on the path, the general public need to be appraised of the danger by a magic sign.

As a person of faith I love the security I find in trusting God. Psalm 17 says "My steps have held fast to your paths, my feet have not slipped" and Psalm 94 "When I said, "My foot is slipping, your mercy and loving kindness O Lord, held me up." That covers both eventualities. I've discovered God's Word to be very thermo-dynamic and I highly recommend it for all conditions.