What to say to soldiers/veterans

[BK_Adores_Chase]

So I'm a cashier and if military personell show their IDs they get a discount.  What can I say to show my appreciation for them serving our country.  I want to say thank you but just because they have an ID doesn't mean they fought, don't some only have an ID for being in the army or whatever?  I don't know anyone in the army or military or whatever should I just say, "thank you for your service" to everyone who shows their ID...if you are in the military what would you appreciate someone saying to you?