A security document, such as a banknote, includes an optical security area having a first periodic optical structure and a security sign provided on the security area and configured to circumscribe a second periodic optical structure which is disposed in offset relationship to the first periodic optical structure. Arranged on the security area is a see-through element for enhancing recognizability of the security sign on the security area. The see-through element defines hereby a viewing zone which covers part of the security sign so as to render this part of the security sign visible by the naked eye.