How to recognise unauthorized opening of our letters? Trassological additions to recognise check-up of a letter. Academic Journal of Internal Affairs, [S. l.], v. 67, n. 6, p. 130–132., 2019. DOI: 10.38146/BSZ.2019.6.9. Disponível em: http://belugyiszemlejournal.pitservice.hu/index.php/belugyiszemle/article/view/577. Acesso em: 28 feb. 2026.