Last time I was in Portugal was many years ago. At that time, airport police openly carried submachine guns. I got into trouble trying to exit the country because I had flown into the country on an airline jump seat (air crew – non-revenue flight), and their customs officers failed to properly document my passport entry record. It was not fun. Foreign police – especially in airports are nothing to make light of. Back then, we'd leave our passports in hotel desk safe to avoid losing it to extremely talented local pickpockets. Best defensive weapon available (other than good empty hand defense skills) is likely a good, heavyweight flashlight – doesn't arouse undue levels of attention and makes an excellent improvised impact weapon. High intensity LED lights available these days also allows you to illuminate darkened areas before you enter them. Just like being in the U.S. – your best defense is complete avoidance of any trouble in the first place!