Not so much an error on the part of the tourism authority...more the tourists who had the bright idea enough times to necessitate a sign.
Photo my own, taken at Saqqara, Egypt. Saqqara is the site of Djoser's (or Zoser) Step Pyramid, which is one of (if not the) oldest pyramid known. Built around 2600 BC, and thus more or less contemporaneous with the beginning of the Mature Harappan!
Not suitable for climbing.