Yes ma'am, I got a gift for NNPS graduation.
I smoked Lucky Strike cigarettes at the time, which are shorter than most cigarettes [except Camels and Chesterfields]. They made these little junior size disposable butane lighters back then that would fit perfectly inside of your LS/MFT pack, after you smoked the first two or three. For NNPS graduation, my dad bought me a silver lighter case that fit over the outside of one of those little junior size disposable butane lighters. It had "Good Job!" engraved on it. At least twenty times a day [maybe more], I'd pull that lighter out and get a pat on the back. I haven't smoked in twenty years, but I still carry that lighter around. My kids and I use it to set off fire works every fourth of July. When they ask what the engraving means, I tell them.
Now hopefully [for his health] your son doesn't smoke, but I'm sure that there's something that he does routinely that you could adorn in some small way. You're his mom. Think about it and give it your best shot. Personally, I might be weary of giving someone something valuable that hangs around his neck when he's working around rotating equipment. To be safe, he'll need to wear it on a breakaway lanyard, which might snag on something in the tight confines of a ship, and result in either a loss or lengthy bilge dive. Also, as twidget it could be a shock hazard if it slips out while he's doing maintenance on electronic reactor control components. Just some things to think about.
He's a twidget. He'll be taking logs all the time. Maybe an engraved ball point pen with several replaceable ink cartridges. He may loose it, but if he hangs onto it for the next five years, it'll mean something to him forever.
Good luck and congratulations on raising a child who's willing to sacrifice six years of his life to keeping us all safe.
Good job,
MGM