It's those innocent, adoring eyes that do it. Or maybe it's the slight tilt of the head or those button noses. Whatever it is, the United States Postal Service's (USPS) new "Neuter or Spay" stamps are destined to be the next surefire hit when they're released nationwide on Friday, September 20.

Attempting to lick the pet overpopulation problem and generate awareness of responsible pet guardianship, the stamps, designed by Derry Noyes of Washington, D.C., feature a male puppy, Kirby, and a female kitten, Samantha, placed against a dark background to emphasize their adorable qualities. Their cuddliness, however, belies their once precarious states: The animals were photographed by Sally Andersen-Bruce in a Connecticut animal shelter while they were awaiting adoption. (Kirby and Samantha were later sterilized and adopted out to new homes.)

Their stories highlight the plight of millions of pets awaiting adoption throughout the country, and of the need to spay or neuter as a preventative part of the solution to pet overpopulation.

"These stamps help us to raise awareness of the benefits of spay-neuter," said Sara Khurody-Downs, president of the new Prevent a Litter Coalition, the coordinating organization of the American Partnership for Pets (APP). "They also provide us with a tangible tool—a unifying and proactive opportunity to make this the moment in America's history when the nation collaborates to raise awareness of the tragedy of homeless and unwanted animals and of the importance of responsible pet ownership."

The American Partnership for Pets, a broad coalition of more than 25 leading animal and veterinary organizations, including The Humane Society of the United States, is the catalyst driving the publicity campaign for the stamp. But the grassroots campaign to actually get the "Neuter or Spay" stamps to market had been ongoing for years. Thousands of animal advocates had lobbied for the stamps since the late 1990s, but none louder than Hope Tarr of the original Prevent a Litter Coalition, who is credited with maintaining the campaign push long after others had lost steam.

Their hard work has paid major dividends. The USPS has ordered a print run of 250 million stamps, far more than the normal run for commemorative stamps—usually around 80 million. While the print run may be unusual, the placement of pets on stamps is not. Dogs and/or cats have appeared on USPS stamps in 1966 (a playful pooch appeared on the five-cent Humane Treatment of Animals stamp), 1982 (a puppy and kitten were featured on 13-cent stamps), 1986 (a puppy appeared on the 22-cent Love stamp), 1988 (several breeds of cats graced the block of four 22-cent "American Cats" stamps), and 1998 (the 32-cent "Bright Eyes" stamp).

The "Neuter or Spay" stamps of 2002 are the first ones to call attention to the issue of pet overpopulation. While the postal stamps themselves do not raise funds for organizations that promote or perform sterilizations, the stamp designs will grace many products that will. APP has licensed the design for use on mugs, T-shirts, tote bags, and pins, among other products; a portion of the sales will go directly to APP. (The products can be purchased via the Off site link below.)

Why is spaying and neutering such an important issue? Because in seven years, one female cat and her offspring can theoretically produce 420,000 cats; in six years, one female dog and her offspring can theoretically produce 67,000 dogs. The HSUS estimates the number of cats and dogs entering shelters each year to be between eight and ten million, with four to five million of those animals being euthanized. There are too many pets and not enough homes.

"Education is key to combating the pet overpopulation problem," said Stephanie Shain, The HSUS's Director of Companion Animals Outreach. "Unless people know the facts about pet overpopulation and sterilization, they are virtually helpless to do anything about the problem. With these stamps, the issue will be highlighted like never before."

Spay or neuter surgery carries a one-time cost that is relatively minuscule compared to its long-term benefits, including the more personal benefits above and beyond helping to curb pet overpopulation. Getting pets spayed or neutered helps them live longer, healthier lives, and makes them more affectionate companions. It will also make them less likely to spray and mark territory, and will eliminate heat cycles. In addition, unsterilized animals often exhibit more behavioral and temperament problems than do those who have been spayed or neutered.

And that sort of education is what the stamps are all about.

"We're looking forward to the day when every pet has a good home and every owner is a responsible owner," Khurody-Downs said. "Hopefully these stamps will go a long way to making that a possibility."

Brian Sodergren is an Issues Specialist in The HSUS's Companion Animals Outreach section.