A dartboard
A dartboard was a target at which a dart was thrown in the game known as darts.
In 2371, after Miles O'Brien asserted that "Darts and bars go together like bacon and eggs", Quark noted that unlike bacon and eggs, nobody had ever come into Quark's and requested to see the dartboard. (DS9: "Visionary")
Later that year, when Quark went on a trip of indefinite length, Miles O'Brien and Julian Bashir attempted to gain entry to Quark's in order to get their dartboard back. When Odo asked them if they couldn't simply replicate a new board, Bashir admitted that they could. O'Brien added that they didn't want to because they wanted their old one, and that Quark should have given them time to retrieve the dartboard. Bashir agreed, saying it was the principle of the matter. Odo then remarked that they might have some difficulty, as Rom had left a complicated lock on the door that would be hard to open.
When Benjamin Sisko arrived, he asked what was going on and Odo explained that they were trying to retrieve some personal property. Sisko guessed it was their lucky dartboard they were after, to which O'Brien replied that they never claimed it was lucky, with Bashir adding that they were used to playing on it. Sisko felt they protested too much. (DS9: "Family Business")