Cat brooch

A cat brooch was owned by the Doctor. He wore it on his outfit and touched it for good luck on occasion where he was to attack something/someone physically. (DW: Attack of the Cybermen)

Behind the Scenes
One idea for the brooch originally was that it would change its expression to match the mood of the current situation, frightened cats when the Doctor was scared. Eventually this idea was dropped. The production team settled for a different cat brooch in the following episodes. Many fans sent cat brooches to Colin Baker; he has claimed to have worn every single one. (DW: Attack of the Cybermen DVD Commentary)