When was the last time you saw a child playing next to a Children at Play sign, rocks falling by a Falling Rocks sign, deer crossing by a Deer X-ing sign… Didn't we all learn the perils of "crying wolf" in kindergarten? Because the warning signs warn of phantom dangers, our brains learn to tune them out. Tom Vanderbilt details the research on this phenomenon very well in his book Traffic.
So what should we do along those rural county roads that have a high proportion of deer/car collisions? I'd like to see a test done where we make up a semi-realistic looking stuffed deer – probably made out of canvas, filled with a lightweight material so it weighs about fifty pounds, with some red paint on it. We have the county public works guys move this around the "dangerous" corridor every few days when they are making their normal rounds. This would provide a real, semi-dynamic warning to motorists that they are on a corridor that has a lot of deer crossings. Or we could train the deer to cross at the yellow crossing signs (apparently under bridges so they won't get wet when it rains).