Phony $100 and $50 bills are flooding the city — and the feds want your help to stop the high-quality fakes.

The funny money, on paper that seems genuine and with watermarks and imbedded strips, looks so real that it can easily fool stores and even banks, they say.

So US Secret Service investigators have circulated posters showing the bogus bills’ tiny imperfections, which include a flawed “T” in “STATES” on the $100 and a minuscule dot inside the “5” on the $50.

Investigators seized $148,000 of substitute loot in New York last week, including $97,000 in a raid near JFK, and $65 million last year in the United States, $10 million of it from Peru.

Genuine notes have small red and blue threads in the paper that look like tiny hairs. The fiber, 70 percent cotton and 30 percent linen, is almost impossible to reproduce, with a slightly rough texture and heavier feel than the fakes, agents said.