The campaign for the largest dog welfare charity in the UK, created by 141 Worldwide, is aimed to encourage dog lovers to donate an average of £15 a month to save a dog's life.
The direct mail pack recreates the cardboard note with a handwritten message on the outside that reads: "Who'd have thought a piece of cardboard could save a life?"
Inside, the donation form takes the same cardboard format and says "Please use this piece of card to save even more lives".
Steve Harding, chief executive at 141, said: "Our vast experience of working with Dogs Trust gives us unique insights into its target audience and how best to communicate with them.
"This mailer adopts an approach that we know to be highly effective, while introducing a fresh creative touch which adds a moving touch of authenticity."
The pack will be mailed to around 140,000 potential donors from this month.
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