At first glance I thought this was a very sensible sign. It is posted near the entrance to an abandoned lead mine in the English Peak District.
I had just been down the mine. It is now a tourist attraction. For a few quid the operators will take you a couple of hundred feet below the ground and give you a long boat ride through a low, dark, dank and narrow passageway to a natural cave way below the surface of the beautiful English Peak District in Derbyshire's Pennines.
The area is popular with tourists and hikers. Of course it is only reasonable to warn the hikers that if they stray from the trail they may receive an unexpected opportunity to take a shortcut to the deepest reaches of the mine, bypassing the booth at which other tourists pay their admission fee.
If you will be visiting the Winnats Pass in Derbyshire and find yourself suddenly at the bottom of an abandoned mineshaft, please call 01623 646333. Oh, by the way, don't forget to take your mobile.