Pubs in Darwin are being hit by an elaborate counterfeiting scam: a couple buying alcohol and cigarettes using $100 notes that have “not for circulation” printed on them in large pink Chinese characters.

Detective Acting Senior Sergeant Glenn Leafe said seven incidents had been reported since Sunday, mostly involving the same man and woman. The scams occurred at different times of day and night.

“The pair collects change from the transaction before quickly leaving the scene,” he said. Leafe said the suspects last struck on Monday at 9.30pm, hitting a licensed premises in Marrara with the unlikely-looking note.

“Upon examining the note staff challenged the pair who fled the store,” Leafe said.

A quick examination would reveal the note does indeed feature Sir John Monash, wartime imagery and approximately the right hues but the likeness ends there. The word “Australia” is largely overwritten with large pink Chinese characters that roughly translate as: “Practising coupon. Sample. For practising use only, not for circulation.”

Such training notes are used to teach foreign bank workers and can be bought online for less than $10.

How the note should look. Photograph: Dan Peled/AAP

Northern Territory police believe all seven incidents are linked, with six of them involving one man and one woman. They don’t yet know where the counterfeit notes were obtained, but are reviewing CCTV footage and expect to catch up with the perpetrators “pretty quickly” to find out.

Leafe said: “This is a reminder for businesses to be vigilant when accepting cash transactions, in particular transactions involving $100 notes.”