Mace them!

I like it. The Massachusetts Bay Transportation Authority is starting a program to promote awareness of sexual harassers on the subway, and get women to report them.

Malikah Fardon-Jones-Finney and her 12-year-old daughter glanced at the ad hanging over their heads at the top of the Red Line train wall.

The image is simple - a young woman squeezed between faceless bodies - and the message succinct: "Rub against me and I'll expose you."

"Does that happen?" Fardon-Jones-Finney asked. "How can you tell when the train is packed?"

Across the way, 23-year-old Olesia Plokhii also gave the ad a once-over and her approval.

"I guess I think it's a proactive idea," she said as she tapped out a text message on her cellphone. "Any kind of awareness around that says 'Perpetrator beware,' I think that's ultimately effective."

The ad - one of at least three posted on Red Line trains - is part of a new public service campaign by the Massachusetts Bay Transportation Authority to increase awareness of sexual harassment on public transit, and to encourage victims to report such events.

Joe Pesaturo, MBTA spokesman, declined to discuss the details of the campaign in advance of the official unveiling tomorrow at North Station. Red Line riders yesterday, however, got a preview of the ads. One shows a security camera pointed into the unknown, with the message "Flash someone and you'll be exposed." Another depicts a lone woman riding the T with the words, "I'm not the one who should be ashamed."