Pink Stamps were trading coupons that rewarded consumers for grocery store and gas station loyalty with free appliances, furniture and other items.
They are the British equivalent to the American Green Stamps, both owned by Sperry & Hutchinson Co.
S&H Green Stamps were the dominant loyalty program of the 20th century.
On the right are a few samples of Pink Stamps. As you can see, they seem to be more red than pink in colour.