Hundreds of thousands of MetroCards are now calling for New Yorkers to register as organ donors as part of a new ad campaign.

The ad, purchased by the nonprofit LiveOnNy, says that "Your signature is more powerful than you think" on the front of 250,000 MetroCards.

The back explains how straphangers can sign up to donate organs. Over 10,000 New Yorkers are currently on a waiting list for an organ, and less than a quarter of state residents are registered.

"New Yorkers overwhelmingly support organ donation, yet too many do not take the important step to register as organ donors," said the nonprofit group's marketing vice-president James Pardes, who said it's unexpected to see the message on a MetroCard.

Queens Councilman Costa Constantinides, who has been trying to make it easier to sign up for organ donation when registering to vote, said MetroCards were an innovative way to reach people on the issue.

"We are currently in a public health crisis," he said. "New York state ranks 50th in registered organ donors."