"No one would have made me a prefect, I spent too much time in detention with James. Lupin was the good boy, he got the badge." - Sirius Black (OP9)
Prefect badges are badges bearing the letter “P” that are worn by Hogwarts prefects to indicate that they are prefects. Badges are sent to new prefects just before they start their fifth year (OP9).
The badges for Gryffindor prefects have an image of a lion and are gold and red (OP9).
Older copies of PS say "Harry noticed a shiny silver badge on his chest with the letter P on it." (PS6)
Newer copies of PS say "Harry noticed a red and gold badge on his chest with the letter Pon it." (PS6)
In OP9, Harry sees the badges which Ron and Hermione get when they become Prefects. It is described as red and gold, and Harry realizes that it’s exactly the same as the one he saw on Percy several years before. So the text has been changed in book one to make the badges identical.