rubber stamp (n.)

• acceptance
• affirmation
• amen
• approbation
• approval
• authentication
• authorization
• autograph
• certification
• confirmation
• countersign
• countersignature
• endorsement
• go-ahead
• imprimatur
• initial
• nod
• okay
• pass
• permission
• permit
• ratification
• sanction
• seal
• second
• sign
• signature
• signet
• stamp
• subscription
• support
• validation
• visa
• vise
• warrant