The MTA is getting serious about subway etiquette as it starts running new ads to discourage bad riding behavior.

The agency on Friday began to put up a new batch of posters detailing a dozen do's and don'ts of subway riding. They were selected from rider complaints to the MTA about the behaviors passengers want banished, spokesman Kevin Ortiz said. The ads will hit the system's 2,600 train cars.

The latest designs for the "Courtesy Counts" campaign target acrobatic subway dancers, nail clippers and train diners, as well as "manspreading."

The ads, Ortiz said, convey "gentle but firm reminders" about common courtesies that make for a more pleasant ride. Other ads cover backpack wearers; people who stand by doors blocking the flow of riders; giving up a seat for disabled, elderly and pregnant passengers; noise makers; litterers; and pole hoggers.

"[Courtesy] takes on an added significance as we see ridership continue to skyrocket in the system," Ortiz said.