It's too casual, dammit! Like saying "excuse me" if you bump into someone.
Consider that you are addressing an individual who has volunteered to risk his (her) right to stay alive. Every day, just read a newspaper or watch T.V. Troops killed in a mortar attack, by a roadside bomb or in a firefight. The war status drags on with no complete closure in sight, perhaps causing our tolerance for these daily horrific events to stiffen. Is it possible to even partially imagine the dread which pervades the family of a service member, to whom every phone call is a potential harbinger of death or injury?
The marvel of it all is the attitude, spirit and sense of duty shared by the troops themselves. True patriots who take pride in their mission and deal with their risk of ultimate sacrifice as the given responsibility of an American citizen. Several tours of duty do not diminish their allegiance. And what caliber of people they are. They truly stand tall. Overriding fear will not be found in their DNA.
There should be an honoring ceremony for every homecoming. Educational and/or employment opportunities should be mandatory. Cutting edge medical treatment should be available, regardless of cost. They must, even in the best of times, never be taken for granted. That's why, when you see a service member in public, don't be shy. Approach and proclaim. "God bless you." It's the very least you can and should do.
Look at it this way: it's because of them that we can indulge in the luxury of addressing life's responsibilities in a free society. They are first class citizens and should be treated as such. It's up to us to always remember and appreciate.