The siglas were primarily used as a signature for family coat-of-arms in order to mark family belongings. The symbols were normally written using a razor on wood, but painting on boats and beach sheds was also a common practice. The purpose of the siglas was to record history and thus they have been ascribed as comprising Póvoa's "writing system". However, the siglas do not record sounds or specific words, and so are not considered true writing. The reason for their prominence has been ascertained to be due to a common ignorance of the Latin alphabet among the local population. Lixa Filgueiras argued that there are two types of symbols, distinguished by their use: the marcas (marks) and siglas. The marks served as a way to register ownership and thus were commonly present. The siglas, on the other hand, were used for magical and religious concerns. The siglas, being symbols of a mythical character, were thus rarer both in their ancient and newer forms. Siglas poveiras have been used for family coat-of-arms since time immemoral by Póvoa de Varzim community. Using these symbols, personal and fishing belongings were distinctly marked and thus a form of property registration. The "marca-brasão" ("blazon-mark") of a family was known within the entire Póvoa de Varzim community and children were recognized by counting the number of "piques" (similar to a traces) within their marks. The usefulness of this system is noticed by its usage amongst merchants in their books of credit, and the siglas were read as we today read a name written in the Latin alphabet. Currency values were symbolized by rings and traces, drawn after the mark of an individual. Nevertheless, it was on the tombs of the dead that the marks acquired a sense of personal significance. It became common and accepted to have one's mark carved onto one's tombstone. According to a former port authority of Leixões, the Count of Vilas Boas, an individual stole a compass in Póvoa de Varzim and tried to sell it in Matosinhos, but he was unaware that the recorded "drawings" in the cover indicated the owner's name and thus the first person whom he approached (a woman from Póvoa de Varzim) managed to recognize the mark immediately. Summoning other fishermen, who also recognized the mark, the thief was apprehended and submitted to the port authority.