The worst thing you can do is display political stuff. The second worst is your hero wall. Mine is as impressive as most, but I've found in 20 years of Dilbert zone, the military stuff takes away more than it contributes. We contributed, and we're a minority. Of those who didn't server, some could not, but far more than you know would not - I call em "Melvins". Even the Melvins who are grateful don't want their noses rubbed in it. More likely than not, Melvin is your boss.

I keep a USS Robert E Lee coffee cup on the shelf above my desk. I wear a miniature pair of submarine dolphins on my collar once a year.