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ST. LOUIS COUNTY, MO (KTVI) – A Jefferson County woman’s Facebook post has set off “alarm bells” in the minds of shoppers, hours before Black Friday shopping.

There’s fear the lure of a $100 bill could cost someone their car.

The Maryland Attorney General had reports of a $100 bill scam around this time last year.

Now, it’s apparently in St. Louis.

At first, Kyri Viehman didn’t notice what someone had slipped under her windshield wiper.

A few Sundays ago, she and her baby son met her mom at the Gravois Bluffs shopping center in Fenton.   They went to Michaels to buy decorations for Kyri’s first family Christmas tree.

Both she and her mother told Fox 2 they came out and found surprises on their windshields.  Neither noticed what turned out to be “fake” bills, until they drove away.

“I was driving down the road.  I saw something flapping.   Then I start driving and see the $100 on it and I was like, ‘oh my God, somebody left me a $100 bill!’” Kyri said.

The idea is for you get into your car, start it, and then notice the $100 through your windshield.

“You leave the car running, open the door, walk over and grab the dollar bill and they jump in behind the wheel and take your car,” Kyri said.

Had she noticed it right away, she could have been a victim, she said.  “I probably would have got out and grabbed it … with the car still running with my son in the back seat.”

Her Facebook post of the fake bill has been shared nearly 10,000 times.

During this season of giving, she doesn’t want anyone to get taken.

“I thought somebody was paying it forward; somebody was like, ‘hey should has a little boy.  Here’s $100 bill.  Have a good holiday,’” she said.

She and her mother said the fake bills had the same message written on them:  “You thought this was real, didn’t you?”

They thought it was just a prank until reading about the scam online.

St. Louis County Police told FOX 2 this was the first they’d heard of it.

There have been no reports to the Missouri Attorney General.