sealed

My lips are sealed. (humorous)

something you say to let someone know that you will not tell anyone else what they have just told you. 'I'd prefer you not to mention this to anyone else.' 'My lips are sealed.'

See also: lip, seal

signed, sealed and delivered (informal, informal)

if a document or an agreement is signed, sealed and delivered, it has been officially signed and completed. A copy of the will, signed, sealed and delivered, arrived at our house the next morning. There was a signed and sealed statement from the prime minister to confirm the treaty had been accepted.

See also: deliver, seal