Thanks to EWI (comment below) for confirming for me what all this 'no flag on the team bus' business is all about. It's nothing other than an insult.
I don't believe that the security threat they're worried about is solely or even mainly one of Islamic extremists. Committed terrorists will know where the US team bus is regardless of what it looks like. No, this is about your average European anti-American protesters, etc.
If security for the US soccer team is that big an issue what does that say about Germany (& Europe generally) that the US flag is the only one that causes this problem. Iran, whose President wants to annihilate Israel? No problem. Saudi Arabia, source for much of the hateful preaching that has helped fuel extremism in Europe? No problem.
If the US players put up with this then they're compounding the insult. I hope at least some of them have the backbone to stand up and say that they won't travel in the bus unless the flag is on the outside. Why should they be treated any differently than any other team?
And, why would the US Embassy go along with this nonsense? That's probably the most nauseating aspect of all of this. I'm fit to be tied.