Sean Penn has goons. Don’t mess with Sean Penn and his goons.

Most major-studio movies that come out in January are, well, not great. After the year-end Oscar push, January is when studios release films that wouldn’t do well against competition. Any competition. This month is a little different for D.C. audiences: First, “Zero Dark Thirty” comes out this week after a limited 2012 release that qualified it for the upcoming Academy Awards. Also arriving this week is “Gangster Squad,” a terribly titled, incredibly cast film whose release date was pushed back from last September because of a scene, since removed, that mirrored the Aurora theater shootings.

“Gangster Squad,” in which the LAPD tries to keep the East Coast Mafia (and, most notably, real-life boss Mickey Cohen) on the East Coast, is a gangster film, a subset of film noir, that magical genre where a saxophone always wails and the sidewalk always glistens. If you’re looking to familiarize yourself with gangster-film tropes before seeing “Squad,” here are some greatest hits. Get it? Hits? Like in the Mob? See, it’s allusions like that you need to watch out for.

“Scarface” (1932)
The year isn’t a typo. Howard Hawks’ film — so brutal that its release was delayed for a year by censors — isn’t as famous as Brian De Palma’s 1983 version, but it’s the granddaddy of all gangster movies. Here’s where you’ll find the driven Mob boss with a soft spot, which you’ll see again in “The Godfather” and “Casino.”

“Dick Tracy” (1990)
If there were an Academy Award for Movies That Aren’t as Bad as You Might Think, “Dick Tracy” might win every year. Using the comic strip as source material, Warren Beatty directs and stars in the film, which takes every visual element of noir (those previously mentioned sidewalks; lighting that lets everyone step dramatically out of a shadow at least once), embraces it and then expands it to an absurd degree. It’s a parody, but — like all good parodies — it intimately knows and respects its source material. Al Pacino’s performance as gangster Big Boy Caprice, right, is essentially Al Pacino parodying Al Pacino playing a gangster.

“The Untouchables” (1987)
We really wanted to write about the Coen brothers’ “Miller’s Crossing,” because we love “Miller’s Crossing.” But to prepare for “Gangster Squad” you need something from the point of view of the cops, and De Palma’s film about Eliot Ness (Kevin Costner) and Al Capone (Robert De Niro) fits the bill. “The Untouchables” isn’t noir — in noir, the detective starts out a little bitter. Here, Ness starts out by-the-book, bright-eyed and bushy-tailed and ends up really not that at all. Not even a little bit.