Why did Billy want to take the cup home without it being engraved?

Billy wanted to bring the cup home for his sister.

Looking at the cup, it seemed that far down in the gleaming shadows I could see two wide blue eyes glued to a windowpane. I knew that my little sister was watching the road and waiting for our return. Looking back at the judge, I said, “If you don’t mind, I’ll take it with me. My grandfather can send it in for me.”