In the early 1990s, the Customs Service began giving anti-drug talks at schools and they would take one of their dogs along to give a demonstration of their abilities. The handlers wanted something that they could hand out to the children and the first trading cards featuring the Customs Service dogs were born.
A second series of 24 cards was released in 1992. Response was so great that another series of 81 cards, these with a blue border, were released in 1994. Series were also released in 1995, 1996, 1997 and 1999. These later series came in packs of four cards.
In 1992, the Customs Service searched for a corporate sponsor to underwrite the expense. Nabisco signed on and one card was included in Milkbone boxes. I do not know if they sponsored the subsequent series.
These cards launched a collecting craze when they came out in the 1990s. The Customs Service repeatedly said that this was a non-commercial venture and that they wouldn't sell the cards. That didn't stop others from selling them. One man even went public with his search, offering $500 for a complete set. Some people began to collect cards which featured a certain breed, while others aimed for cards showing dogs with the highest seizures or those who worked in their hometown.