Smokey bear is a euphemism for a cop, usually a state trooper or county cop (county mounty).
The nickname came into being soon after the US Forestry Service invented the cartoon character Smokey Bear. The cartoon bear wears the classic straight brimmed ranger hat, the same as many police officers. It is an easily identifiable (and patently ridiculous) symbol of law enforcement personnel in the US. Truckers spend large amounts of effort finding out where Smokey Bear might be working or running a speed trap. They use radar detectors (fuzz busters) or use CB radio to rat out the bear's location. Truckers live by the credo Don't feed the bears.