Decoration process of a visible lamina of an adhesive unit consisting of: preparing a transparent sheet (2) having an outer face (2a) suitable to constitute a visible face of the adhesive unit and an inner face (2b) opposite the outer face (2a); and decorating by means of a first decorated layer (3) applied to a portion of the inner face (2b) defining at least one area free of the first layer (3), and a second decorated layer (4) structurally different from the first layer (3) and applied to at least part of the at least one area free of the inner face (2b).