Officers are appealing for information following reports of a theft in the Trafford Centre on 4 March.
A teenager had bought a gift from Pandora for his girlfriend, along with a pack of 5 Pink Floyd-branded guitar plucks.
When they entered a store for food, they accidentally left the bag behind, only to return minutes later to find that it was no longer there.
It is believed that someone picked the bag up and hid it within their own shopping.
Officers have now released images of a man and a woman they would like to talk to, as it is believed that they could help with their enquiries.
Anyone with information is asked to contact police via 101 or our Live Chat service at gmp.police.uk, quoting crime reference number CRI/06MM/0003348/25.
Alternatively, you can contact the independent charity Crimestoppers, anonymously, on 0800 555 111.
