The Red-Headed League was a fictional organization that employed Jabez Wilson in the Sherlock Holmes short story "The Red-Headed League".
In 2365, Data, while masquerading on the holodeck as Sherlock Holmes, noticed a bell cord hanging in front of the door of the home of the Red-Headed League shortly after witnessing a thieving boy running away, and, from these three things, was able to deduce that Wilson was the intended target of a murder. (TNG: "Elementary, Dear Data")