On display at the National Postal Museum in Washington D.C. is Owney the stray-mutt-turned-postal-mascot.  As story goes, Owney the pup wandered into the Albany post office in 1888.  He was cute and sweet and liked the smell of mailbags, even following them into the railcars.  In fact, Owney travelled the rail across the country with the mail, and since no train every derailed (a common disaster) while he was a passenger, he was adopted as mail mascot.  In 1895 Owney even made an around-the-world trip, traveling with mailbags on trains and steamships to Asia and across Europe.

But Owney grew irritable with age.  He bit a reporter and was shot only June 11th, 1897 in Toledo.  Despite that unfortunate hitch in the Disney-esque story, everyone loves a stuffed mascot, so off Owney went to the taxidermist along with his jacket custom made when the dog tags he was given on his travels began to weigh down his collar.

http://www.postalmuseum.si.edu/exhibits/2c1f_owney.html