More than $300,000 worth of stamps have been stolen in a series of "unique" break-ins at Sydney post offices, with NSW Police releasing CCTV images of the suspects.

Police said the stamps, along with cash, mobile phones, SIM cards and other stock had been stolen in more than 20 break-ins since March 2013.

CCTV footage has been released of two men as part of an appeal for information.

Post offices at Alexandria, Artarmon, St Peters, Crows Nest and Kingsgrove have been targeted.

Strike Force Ingram was set up to investigate, and anyone with information is being asked to contact Crime Stoppers.

Police said while the two people filmed on CCTV have their faces concealed, it is hoped someone will recognise them.

Redfern Region Enforcement Squad investigator, Acting Sergeant Kath Griffin, said investigators believed the incidents were linked.

"In addition to similarities throughout the break-ins, the targeted theft of postage stamps is unique," she said.

"The men depicted in the footage appear to be the same two men and, while they have their faces concealed, we are hoping someone may recognise one or both by their eyes, stature, walk or the way they move".

Acting Sergeant Griffin said it was unclear exactly what the thieves were doing with that amount of postage stamps.

"That's the $300,000 question. We have no idea at the moment of what the two males that committing crime are doing with the stamps, so that's why we're appealing to the public to contact us if they know anything."