A Brief History of the Marque
Built by Fratelli Possio of Turin, their first motorcycle was of 125cc. This was followed by a 150cc fourstroke OHV model. In 1929, a 175cc ohv model appeared with chain drive replacing the belts used on earlier machines. The designer was Alberto da Milano, hence the acronym Posdam.
A Facebook group post shows a 1924 OHV 125cc belt-drive model.
Sources: MC Storico Conti, Tragatsch p251.