I hoped to sign the birthday card our team bought for Coach, but I couldn’t find a spot to sign my name because someone went all John Hancock on it and signed his name across the whole card.
Reference to: ________________________________________
Possible meaning: ____________________________________
Reference to: John Hancock
Possible meaning: "John Hancock" refers to the American statesman who famously signed the United States Declaration of Independence with a large and prominent signature. In this context, it means that someone signed their name in such a bold and dominating manner on the birthday card that there was no space left for others to sign their names.