[mattzito]

The whole originating notion of a passport was to say to other countries, "This person is a citizen of our nation in good standing, and we vouch for him".

Other countries can look at that passport and make their own decision - for example, I've anecdotally heard from people that having a passport stamp for Israel can make border crossings into certain middle eastern countries much more complicated.

Now, the US in effect is saying, "We believe this person to be a bad guy, and you should not trust him". Since he has been charged with a number of crimes, this is a fair statement.

This is the same thing that happens with people in the US who are considered a flight risk from prosecution - their passport is flagged and they are required to turn it in.

One of the many reasons why Snowden's behavior in first revealing himself then leaving hong kong to Russia is very odd is exactly this - how could he not know they could revoke his passport? What did he think would happen?