The I-Spy books were basically children's activity books. They were promoted by the News Chronicle and cost 6p (2.5p) each. The idea was to tick off the items depicted in the book when you had seen them. I-Spy "On the Farm" listed various animals and farm equipment you might see on a farm, and the idea was to check them off as you saw them.
The I-Spy Club had a Native American theme, with Big Chief Eagle Eye presiding. You could be sent headdress feathers for various achievements such as recruiting new members. The newspaper column featured exciting things like writing in code by putting the last two letters of a message at the front, but keeping the same number of letters in the words. Thus "good hunting" became "odhu ntingo," which the big chief regularly signed off with.
As children my friends and I were avid members. Having obtained "I-Spy Ships and Harbours," we undertook the long walk along the seafront to Grimsby docks and duly ticked off the various fishing ships we saw there. We entered a fish warehouse, and solemnly presented our I-Spy badges and books. The fish merchants took us under their wing and pointed out the various different fish, which we recorded in our books.
One merchant enthralled us as we sat amongst his wooden boxes filled with gleaming fresh fish topped with ice. The important thing to remember, he told us, is that "Ernest West sells the best." His name was painted over his corner of the warehouse. We practically filled our I-Spy books, and when I wrote to Big Chief Eagle Eye to tell him about it, he sent back a feather to congratulate me on such a "red letter day."