Abstract: An anti-theft seal, particularly adapted for application to slender parts of products such as earpieces of eyeglasses, which comprises two complementary jaws, which are provided, on opposite sides of a central part thereof adapted to grip a product, with elements for mutual retention which can be deactivated by magnetic action, at least one plate, which is connected to at least one first one of the jaws, in the central part, so as to tilt with respect to at least one extraction direction of a slender part of product which during use is comprised between the jaws, for the jamming of the plate against the slender part upon an attempt to extract it from the anti-theft seal.