The invention relates to a gasket seal (1) in the form of a profile comprising a U-shaped groove (23), which is intended to claim the edge (9) of the window (3) and a flexible masking lip (25) which is used to conceal the gap (8) between the window and the body (5). The inventive seal also comprises a longitudinal rib (29) which is provided with local deformations (30) that act as positioners (17). The method of producing the aforementioned gasket seal comprises a step involving the extrusion of a profile which comprises a U-shaped groove, a flexible masking lip and a continuous longitudinal rib and, subsequently, a step whereby said rib is deformed locally in order to form the positioners. During said deformation step, the rib is flattened locally by a crushing or pinching in order to reduce the thickness thereof and increase the height of same in the relevant area. The invention is particularly suitable for manufactures of motor vehicle accessories.