New London — Police are warning local businesses and citizens to be cautious of counterfeit cash being circulated in the area.

Police said in a statement Thursday that they are investigating an incident on Wednesday involving counterfeit currency in which 13 $100 bills were seized. The Secret Service was notified and is assisting with the ongoing investigation, police said.

Police urge members of the public to contact the police immediately with any suspicious or counterfeit currency.

Citizens should be aware of three security features located on currency: color-shifting ink, security threads and watermarks.

Color-shifting ink is located on the dollar amount on the face side in the bottom right corner. The color-shifting ink can be found on $100, $50 and $20 dollar bills series 1996 and later, and on $10 dollar bills series 1999 and later. The color originally appeared to change from green to black, but it goes from copper to green in recent redesigns of the bills.

Security threads are embedded in the paper of the bill and run vertically through the clear field to the left of the Federal Reserve Seal. On authentic bills, this should be easily visible when held up to light.

Watermarks are located on the face of the bill on the right side. Use natural light to see if the bill bears an image of the person whose portrait is on the bill. Hold the bill up to a light to check for a watermark. A watermark bearing the image of the person whose portrait is on the bill can be found on all $10, $20, $50 and $100 bills series 1996 and later, and on $5 bills series 1999 and later. The watermark is embedded in the paper to the right of the portrait and should be visible from both sides of the bill.

Anyone with information concerning counterfeit currency is asked to contact the New London Police Department at (860) 447-5269, ext. 0, or anonymous information can be submitted via the New London Tips 411 system by texting NLPDTip plus the information to Tip411 (847411).

For more information visit bit.ly/SScounterfeit.