Police are warning business owners to beware of counterfeit money in light of four cases of fake $50 bills being used in Utah County in the last week.

Three of those cases occurred at Provo convenience stores, said Provo police Sgt. Nisha King on Friday. The bills passed in all four exchanges had the same serial number printed on them: CG11392396A.

King urged businesses to use a verification pen to determine that bills are legitimate to avoid future cases like these. The ink in verification pens turns a certain color when it reacts with legitimate bills, and turns a different color when the money is counterfeit.

If stores make the mistake of accepting the fake money, King said “ultimately, it’s the business that will be at a loss.”

She’s heard of other cases of counterfeit money where a person alters a legitimate bill to create a fake bill with greater value, such as making a $10 bill look like a $50.

In addition to using the pens, clerks can sometimes be tipped off to counterfeit money by a “different” look and feel to the bill, King said.

Security measures for $50 bills include color-shifting ink, a portrait watermark of President Ulysses S. Grant, a security thread that can be seen when the bill is held up to a light, raised printing and microprinting of the word “FIFTY” along the borders of the note and “THE UNITED STATES OF AMERICA” in Grant’s collar.

Identifying characteristics for other bills can be found on the website for the U.S. Currency Education Program.