The bulletin says, "Officers should look for rope burns, unusual bruises, wounds/scars or other evidence that they engaged in paramilitary training..."
The unusually specific internal warning, obtained by CBS News, covers customs checkpoints at three East Coast airports -- New York's Kennedy, Newark, and Washington's Dulles, as well as international airports in Detroit, Chicago (O'Hare), and Los Angeles (LAX).
Recent Pakistani military raids near the Afghan border, the warning says, "...documents the terrorist related threat posed by individuals traveling to train at terrorist camps in Pakistan."
Intelligence officials describe them as general "Jihadist camps" -- less sophisticated than these training operations once run by al Qaeda in neighboring Afghanistan.
Sources say there is no hard intelligence connecting the Pakistani camps to any imminent threat against the U.S. But the Customs bulletin concludes, "...it is reasonable to expect that many of the individuals trained...(there)... are destined to commit illegal activities in the United States."
At the same time, U.S. officials have moved to ban foreign pilots with possible ties to terror groups. Sources say at least eleven pilots -- most of them Saudis -- have now had their licenses revoked by the FAA.
The 11 were identified when more than 450,000 pilot names were crosschecked against terrorist watch lists.
All of this comes as security officials prepare for the July fourth holiday -- a period they've identified as high-risk. Still there are no plans -- at the moment -- to raise the nation's terror threat level.