Counterfeit $100 bills are popping up around Tracy and police want local merchants to be on the lookout.
In the last week, bills were used to make purchases at a fast food restaurant and a local electronics store.
"People need to be aware they are out there," Detective Alex Neicu said. "It's not isolated to Tracy. Someone is flooding the market with fake $100 bills."
After examining the quality of two bills recovered by police on Wednesday, Neicu said it was obvious that the bills were manufactured by different people.
"One is ingenious, but not up to par and the other is fairly high quality," he said. "It's probably the highest quality I've seen in Tracy."
A store manager at the Radio Shack on Tracy Boulevard said he received four of the counterfeit $100 bills last Sunday, when a man came in to purchase a camera.
Neicu said often people looking to pass a fake bill would target businesses that are busy or have untrained employees.
Authorities said there are various methods that can be used to make a fake bill, but the most common is a bleaching method.
By bleaching the ink off a real five-dollar bill, police said counterfeiters are then reprinting a $100 bill image onto the paper using computer technology.
This method can sometimes fool the counterfeit pen used by many businesses to determine if a bill is real. By marking the paper, the pen will leave a brown mark that shows it's genuine.
Although it looks legitimate to the naked eye, the fake bill still retains two of its security features -- a Lincoln watermark and five-dollar security thread.
Imbedded in the paper, both security features are visible by simply holding the bill up to a light.
Considered a violation of state and federal laws, each bogus bill is turned over to the United States Secret Service.
Although counterfeit bills are common in denominations of $10 and $20 bills, fake $100 bills are becoming more prominent.
"It's not unique, we are seeing a lot of bleached five dollar bills," Sacramento Secret Service agent Brady Mills said. "That's why there are changes in the currency every seven to 10 years."
Utilizing a counterfeit database, secret service agents are able to track fake bills across the country. Neicu said often counterfeiters would use the same bill over and over again during the printing process, which means each bill will have the same serial number.
Anyone who is in possession of a counterfeit bill is urged to contact his or her local police department or secret service office.
Contact reporter Denise Ellen Rizzo at firstname.lastname@example.org.