"The left hind foot of a rabbit killed in a country churchyard at midnight, during the dark of the moon, on Friday the 13th of the month, by a cross-eyed, left-handed, red headed bow-legged Negro riding a white horse - this we do not guarantee."
This was a quote I found in "The Oxford Dictionary of English Folklore" by Jacqueline Simpson and Steve Roud.
For some unknown reason, during the twentieth century it became lucky to carry a rabbit's foot (I like borgo's suggestion) despite the rabbit's ancient association with ill luck and death. Advertisments such as the one above began to appear in large amounts in British magazines and newspapers.
The rabbits were killed in America by a man who may or may not have been a Negro. If so I seriously doubt that he was red headed. The same goes for him being mounted, as sitting upon a horse would make it quite difficult to kill the rabbit. They were killed at all times of the month, probably in some kind of abattoir. Their left hind feet were then mounted in silver and shipped to England where they sold by the thousands.