Laje dos Sinais is the name given locally to an extensive flattened boulder where geometric and proto-geometric figures were engraved that represent a historic panel whose meaning is unknown, perhaps related to the solar cult.
No information.
Source: http://www.portoenorte.pt/pt/o-que-fazer/laje-dos-sinais/
Image source: Gabinete de Turismo e Artesanato de Barcelos