Which is why detainees held at Guantanamo Bay have all had their individual circumsances reviewed by a military tribunal.

Right, in cases of doubt, you're presumed a POW until the court or tribunal finds otherwise. In the field, that could be a rather rough-and-ready procedure. Of course, prisoners at Gitmo have not been "in the field" for years.

1) What "fixed distinctive sign recognizable at a distance" do U.S. troops wear?

Never failing to side with terrorists

The conventions do cover resistance fighters and others who may not wear regular uniforms because they don't have any, however, they must bear their arms openly in plain view to indicate they are fighters and not innocent civilians. In my opinion, the Taliban who carried arms openly were clearly under Geneva POW coverage. The conventions also say (IIRC) that where doubt exists, a military court must determine, on a case by case basis, whether the combatant was within the spirit if not the letter of the law.

Most Al Qaeda operatives, on the other hand, are clearly outside Geneva Convention protection.

If you're part of the armed forces of a Party to the conflict, you don't have to be in uniform, etc. -- those criteria are for "other militias," etc. not part of said armed forces.

That would seem to handle my Taliban example. And I see that Glazier & I agree that terrorists are simply criminals.

To argue that the Taliban's soldiers, for ex, weren't "soldiers" under Geneva just seems too cute.

The conventions were evidently drafted by European powers used to dressing up their soldiers. The French still had those red pants back then, right?

...the essential right of a combatant is authority to kill the enemy on sight and destroy his war material while enjoying complete immunity from domestic laws while doing so. In exchange for the this immunity, the combatant is himself subject to being shot on sight. While his surrender must be accepted if offered, an adversary need not offer the enemy this opportunity before attacking, unlike law enforcement personnel who must do so.

So, when does a criminal become a terrorist? Who gets to decide when someone has to be arrested and/or subdued and when they can be shot on sight? Cops? The military? DHS? Clearly, an insurgent in Iraq setting up an IED or mortar shot on US/Iraqi forces is a terrorist, but what about a guy mugging an off-duty soldier in Cleveland? Or someone stealing a TV out of family housing on a base?

The problem is that these treaties were written to deal with actions in a combat zone, not in a civilian city thousands of miles away.

Uniforms, rank insignia, unit patches, an American flag patch, and a patch that says "U.S. Army" or the equivalent.

At what distance?

Presumably, the distance from which you'd recognize a man.

Recognizable to whom?

Pretty much anyone. An American soldier in full battle rattle would be instantly recognizable as a soldier by just about anyone who had ever seen a war movie, a soldier, or the news. As opposed to, say, a terrorist dressed to blend in with the crowd so as to surprise unsuspecting civilians.

(2) If regular-army troops commit war crimes, are they no longer POW's?

That said, I think the Dix Six (or Six Dix) were criminals, not POW's.