Interesting question. I am from Europe/Germany and i donīt know why it should be more dangerous to wear a PAM in an european city than in an american?
Every bigger city has its problem districts but i assume thatīs the same over the ocean and if you plan to visit some place like the Frankfurt "Bahnhofsviertel" it should generally a good idea to keep attention
Sorry, donīt know the english word but its the place around the main train station in Frankfurt/Main where the drug scene is very present.