Upside Down Warning

This afernoon on Dartmoor I came across this upside down sign. 

P.S. Although it can be clearly read if you stand on your head, there are, as other blippers have pointed out, some inherent dangers in doing this! It baffled me initially, but there seems to be a simple explanation. Signs like this with red and white enamel paint on heavy steel were once fixed to telegraph and electricity poles on British Rail. This shot was taken beside a disused railway line. It would appear that an old pole was used here as a corner post without removing the sign. Mystery solved,  I think!