Complex sentence: In the past, the siglas were also used to remember things, and they have been known as Póvoa's "writing system", used because many fishermen did not know how to write in the Latin Alphabet, and thus acquired great utility.
Split into simpler sentences: In the past, the siglas were also used to remember things, and they have been known as Póvoa's "writing system". Used because many fishermen did not know how to write in the Latin Alphabet, siglas thus acquired great utility.