What was hidden in the pendant that day's father gave him

I'm not sure if this helps,

He remembers how he got it. When Day was a child, his father - who had a secretive job involving the Colonies - found a United States quarter from 1990 in a swamp. Day’s parents were very excited about it because it proves that the Republic and The Colonies were once one country - history the Republic suppresses to remain in power. They decided to weld it into a piece of metal and make it a pendant for Day, believing that hiding it in plain sight would be more secure if they got raided.