The US Customs folks, who now are under the Homeland Security umbrella, are one of the only agencies able to do warrantless search and seizure. They ask if they can look at your bag, but this is faux courtesy and to look at your demeanor if you refuse. They can certainly confiscate the cigars, banded or not, and do not have to prove anything - you can dispute them, but it is a process that goes on while your cigars dry out in a holding cage somewhere - just follow the smoke.
If the embargo gets lifted, the novelty effect will prop up prices for a little while, but eventually cigar buffs in the know will realize that the consistency of cubans has suffered, and that there are some pretty decent alternatives out there right now. Production will have to go up, and quality will likely go down. Many cubans are still among the best, but I glad to say that some US available cigars give them a run for the money. I had some nice ones while in Vancouver last year, but paid approx $30CDN each, and used them up in Canada. What a shame.
In the past two years, I have heard of three seizures of contraband smokes within the US. A recent one was a raid on a couple of customer humidors in NYC (maybe Club Macanudo, maybe not - no offense meant if I am mistaken on the name of the place). I thought I heard that some other patrons sticks were seized also - sort of "Habano by association". Did anybody hear the same?