I mailed a bunch of club magazines out and instead of waiting in the long lines at the post office I decided to buy the priority mail stamps and mail them that way. I got them back with a green sticker on them that said:

"We regret that yor mail is being returned to you because of heightened security measures. All domestic mail, weighing 16 ounces or over, that bears stamps and all international and military APO/FPO mail weighing 16 ounces or over, MUST be presented to a retail clerk at a post office. Postage that is affixed to the returned mail may be used for re-mailing the item."

They also had a picture of an airplane on them in a circle with a line through it saying "Surface Only."

Amazing. Had to stand in line to see a clerk so they could be mailed properly.