Stamps on a passport is actually a pretty good example on what one would like to hide from the authorities even though he didn't do anything wrong. I say that as an answer to people like Eric Schmidt who say that if we have something to hide, we shouldn't have done it in the first place. Well, that would be true in a perfect world, but here we have a perfect example that it's not the case. So for this case, I would also advise having multiple passports.