Racing pigeons...

"I rode over the mountains to Huddersfield (Yorkshire). A wilder people I never saw in England. The men, women and children filled the streets and seemed just ready to devour us."
John Wesley


I live close to the centre of Newcastle upon Tyne, right next door to a Working man's club (clerb) There is a huge fraternity of racing pigeon fellas around and about and their truck for transporting the pigeons to their starting destination is always parked beside my house. When they clean it out we always find these little metal tags on the pavement...I've always assumed they are placed on the baskets that hold the pigeons before they leave and are cut open at the start of the race but maybe someone can enlighten me.