It means not giving anything away. It is known by 1782 and derives originally from the expression to seal up another person's lips or mouth, to prevent him betraying a secret. A seal is a device, such as a heraldic design, impressed on a piece of melted wax which then hardens. It is used to close up a document as evidence of genuineness, or as a mark of ratification or approval.

Übersetzung:

meine Lippen sind versiegelt

Gegenteil(e)

The opposite of "my lips are sealed" is "to be indiscreet".

Synonym(e):

You could also say: I will not discuss or reveal a particular secret.