Trespassers' Society
This was formerly called the Ankh-Morpork Explorers' Society, until forcefully reminded by a post-imperially minded Patrician (Vetinari), that the name was a misnomer, as most of the places "explored" by Ankh-Morpork's finest and in many cases subsequently claimed for the Empire already had people living in them, from whose point of view the explorers could justifiably be called trespassers.
As mentioned in the book Unseen Academicals