Drug dealers take note: Potheads aren’t the only ones who know what 420 means.

Quincy police arrested a man advertising his wares with the words “420 help is here” on the online classified site Craigslist. Drug detectives knew that in the cannabis culture, 420 means getting high on marijuana.

The Craigslist item said “Give me a ring if you need some help,” and listed a phone number, which a detective called Friday.

He told the man who answered, later identified as Christopher J. Gray, 30, of Marlboro, that he wanted to buy a quarter-ounce of marijuana. A meeting was set up for later that day in a parking lot on Southern Artery.

Gray was cautious when he met two detectives posing as customers, and asked if they were cops, police Capt. John Dougan said. Apparently satisfied when the officers said they were not, Gray allegedly said: “Well, I trust you. You look normal,” and sold them a small bag of marijuana for $45.

Gray pleaded innocent at his Quincy District Court arraignment Monday to marijuana distribution and marijuana possession charges. He was told to return to court July 8.

There have been other cases of Craigslist being used to sell drugs locally. Hanover police responding to two Craigslist ads for marijuana arrested four people in March 2006.