What garnish is used in a Gibson martini?

In a Gibson martini, the traditional garnish is an onion, specifically a pickled cocktail onion. This choice of garnish distinguishes the Gibson from the more commonly known gin martini, which typically features an olive or a lemon twist. The use of an onion not only provides a unique flavor profile but also adds to the cocktail's visual appeal, lending it a slightly different character than other martini variations. The onion accentuates the dry, clean, and herbal notes of the gin, making it an integral part of the cocktail's overall tasting experience.