In the moutains of the national park and then on the drive in the moutains (where the 1984 wWinter Olympics were) there were a LOT of these signs. Sometimes they would be next to other signs, then they made sense. Like No Passing... ! or 30 KMP Curve... !
But my favorite was when they were like this. Absent context with just a !
It is totally the chicken with its head cut off scream. Watch Out!