Holmes' tie pin
A tie pin was a small piece of jewelry used to fasten a necktie.
In one of Arthur Conan Doyle's Sherlock Holmes stories, Queen Victoria gave Holmes an emerald tie pin as a reward for solving the theft of the Bruce-Partington plans.
In 2365, Data showed Geordi La Forge this object as an example of the collected possessions Holmes considered significant. (TNG: "Elementary, Dear Data")