A Royal Mail bag containing special delivery post was stolen from an insecure hire vehicle parked at the Royal Mail depot in Abbotsbury Road, Weymouth on 17 December at around 5.20pm.
Sergeant William Taylor, of Weymouth police, said: “I am appealing for witnesses and anyone with information about this incident to contact Dorset Police.
“I would also urge anyone who has seen discarded Post Office marked material in the local area to call me.
“All calls will be dealt with in strict confidence.”
Witnesses and anyone with information should call Dorset Police in confidence on 101, quoting incident number 18:147. Alternatively, call the free and anonymous Crimestoppers line on 0800 555 111 where mobile phone tariffs may apply.