prayer in schools breaks the rules

If we’re not supposed to have prayer in public school, why does the electronic marquee outside my daughter’s middle school proclaim, “God Bless Our Troops”? Don’t get my wrong - I’m not a God hater, or an atheist, or an agnostic. I’m Catholic, and I attend church regularly. I like Jesus. We pray at our dinner table. I’m just wondering why this is allowed when prayer in school isn’t. Is it because the sign is outside? I’m thinking not. How long til someone makes a stink about it? (I’m tempted to