IMHO, that's easier said than done, especially on subways, trains, and busses. For example, the #64 bus in Rome is nicknamed the Pickpocket Special. And the elevators at the Eiffel Tower have "Beware of Pickpockets" signs.
I agree - you have to be very careful, carry money in a money belt, but still could be a victim. Places get very crowded, you get pushed, and whatever is not attached to you is gone.
DH was a victim on the #64 bus in Rome. And we are pretty careful. DH carries credit cards and most money in a money belt, under clothing. The day's admission money, lunch money, etc. (never over $60) is in a wallet that he keeps in his pocket, his hand over it. A choice to trade security for convenience.
The #64 is sooooo packed and the thieves are good - the person got the money but not the wallet. DH was holding onto a pole with one hand, got bumped hard, hand moved from wallet, felt pressure on his wallet, put his hand down as soon has he could and the wallet was there. Went to get money at the Colliseum, and no money in the wallet. Luckily, the big stuff was in the money belt where no one could get.
This was one time in 20 years of travel to Europe. Sure we looked and acted like Americans - we speak English to each other when travelling. And at 6'5", DH is taken for a local only in Holland and Scandinavia, not Italy or Spain.