a slogan used by politicians and corporations to get support for a war they will never fight in. Also used to sell bumper stickers, car magnets, all that shit. This slogan is said by people who have no inkling what it's like to serve in the Armed Forces.
Gina's car has a "support the troops" bumper sticker on it. It's there because it's the fashionable thing to have on a car these days.