On our recent return from Portugal we experience a disturbing occurrence which may be a warning to others. It was a quiet Sunday morning when we left Soa Domingos near the copper mines, and we had a very good drive North up the N122. Then a car passed us with hazards flashing and slowed down indicating we should stop. Remembering all we had learned, I overtook and kept going while checking rear view camera and mirrors to see if anything could be wrong. All seemed OK and the car passed us and accelerated away. I have no way of knowing the intention of the driver but decided not to take a chance and stop. I did stop to check once we were in a built up area and all was well. We thought travelling on a quiet Sunday morning would be good but maybe not a good idea on quiet roads. I am relieved we had no further cause for concern and soon we were close to a larger town and the offending car did not re-appear. I am now considering one of the in car cameras that can record these type of incidents and although not much of a deterrent you can check afterwards and I suppose report the incident if you felt like it. Be careful out there and don't trust anyone.