Pink Stamps were trading coupons that rewarded consumers for
The British equivalent of American Green Stamps, both Pink Stamps and Green Stamps were 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 color.
For more information on Sperry and Hutchinson, there is a small article on Wikipedia.