The sign looks like those posted along railroad rights-of-way. “Visitors may ... encounter vehicles traveling at high rates of speed.” This is another kind of railroad, one that transports illegal drugs (and the money that comes with them, there’s LOTS of money in drugs and who knows what it is funding?) and crime.
So BO’s policies appear to be creating and protecting a railroad that transports drugs, drug money, and crime. It’s a clear right-of-way from the border to Phoenix in AZ, from Tijuana to San Diego in California, etc.