Police in Horncastle say they received reports of attempts to use forged £50 and £20 notes to pay for goods at Post Offices, stores and possibly public houses and eating establishments in the area.
Police warn the offenders may also ask for notes given by the cashier as change to be exchanged for smaller denominations.
Offenders place the real notes in their pocket / wallet /purse and then pull out more forged notes to make the exchange.
Police say some of the individuals appear to have Irish connections and are possibly driving on Irish registration plates.
*If you have witnessed and or heard anything suspicious - or have information - call 101 quoting incident number 308 of 14/07/2018.
Alternatively, call Crime Stoppers UK on 0800 555 111.