Portuguese term (edited): serrilhas antiviolação

"SERRILHA
Sequência de pequenos furos ou cortes muito unidos que, em folhas de papel, servem para facilitar o seu corte manual.

A serrilha é utilizada em materiais como postais, folders, ingressos, cartões, tags e outros. Este acabamento é de uso prático, sua função principal é de facilitar o corte."
https://instrucoes.atualcard.com.br/montagem/serrilha/

photo of letter card with perforations: https://en.wikipedia.org/wiki/Postal_stationery#/media/File:...

"Although the tamper proof lining does make the envelope satisfactorily opaque, the envelopes easily open and it has become clear that it will not remain sealed if put through the mail. Even when the glue keeps the end of the envelope sealed, the easy open perforation tears and the envelope arrives COMPLETELY OPEN. This has happened numerous times. I will be forced to tape closed the entire top portion of the envelope for the rest of the ones I have, but I will not be ordering these again" (emphasis added). -
https://www.staples.com/Staples-EasyClose-Tamper-Evident-Sec...