Which NFL team's helmet famously has no logo on it?

Which Cleveland franchise returned to the NFL as an expansion team in 1999? Which team is named after its founder and first coach, Paul Brown? Which team did Paul Brown found after leaving Cleveland? Which team was founded and coached for decades by George Halas, known as "Papa Bear"? Which team's helmet logo appears on only one side of the helmet? Which team's primary logo is a star? Which team uses a lightning bolt as its logo? Which team's logo is a fleur-de-lis?