Watch thefts have increased significantly in Europe over the last 10 years. Especially violent robberies on the street.
However, you still see many valuable watches on people's wrists in historic centers.
Is it safe to wear a Speedmaster while traveling in Europe? I would say yes, although it is necessary to distinguish situation by situation.
Better in winter than in summer (watch covered by jacket), better steel than gold, better in the evening than during the day, better in a group than alone.
From what I read, violent thefts occur more often against lonely people (for example walking the dog), or in seaside places, where there are organized gangs, especially from Eastern Europe, and they are also concentrated towards sports Rolex, Patek and other quickly sellable watches.
I read that on the black market the price of a stolen watch is around 30% of its street value. Maybe stealing a Speed isn't that convenient for a thief.
I use my Speedmasters every day and also other valuable watches when I travel, but I also bring a nice Seiko with me if I have to visit some popular neighborhood or go for a trip to the beach.