In this Jan. 11, 2010 photo, a worker shows a marijuana bud for sale at the Lotus Medical dispensary in Denver. AP WASHINGTON (Reuters) - District of Columbia Mayor Vincent Gray on Monday signed a bill that decriminalizes possession of up to an ounce (28 grams) of marijuana in the U.S. capital, a spokeswoman said.

The law makes possession a civil violation with a penalty of $25, lower than most city parking tickets. Possession had been a misdemeanor carrying up to six months in jail and a $1,000 fine.

Proponents had backed the measure as an issue of fairness. A study by the American Civil Liberties Union had shown that blacks in Washington were eight times more likely to be arrested for pot than people of other races.

(Reporting by Ian Simpson; Editing by Scott Malone)