Learn to read the medals and insignia on the hat and you will know. The red orange green Vietnam medal just means that they served in the theater. An arrowhead on the Vietnam ribbon means they were on the front lines (but lacking it doesn't mean they weren't.) A silver star ribbon (blue white red white blue) means they did some outrageous shit. A bronze star (red-white-blue-white-red) means nearly the same thing, especially with a V pinned in the middle (for valor in combat.) The other stuff gets down into the weeds, but the only ribbon (AFAIK) with purple on it is a Purple Heart, and you can't miss it, it's all purple. You also need to realize that "in combat" is a grey line. My grandfather stood by the door in Westmoreland's plane with a pistol while they base they were at was being attacked. He never fired it. Does that count as combat? My business mentor was inside the tail of a C-130 trying fix the hydraulics so they could get off the ground while a mortar attack was going on (hence the need to get off the ground.) While he's in there, watching shrapnel make a little light show by punching tiny holes in the hull, was that combat?