The Society of Owls is a secretive organisation featured in the Return to Canifis and Legacy of Blood novels, and does not currently appear in game. They are an ancient organisation, tasked with protecting Misthalin from the ongoing threat of Morytania. The organisation's symbol is described as an owl, with its wings outstretched, and its head turned the other way round.
Its members carry wolfbane daggers, and appear to have authority surpassing the Varrock Guard. They are given the power by King Roald to do whatever is necessary to get their job done, including detaining witnesses of the Wyrd attack.
To join the Society through the usual channels, the members have to have lost a family member to the forces of Morytania. This requirement is waived for the role of archivist though, as Reldo states in Return to Canifis.