I hate to say it, but something that has "woodsy" look to it, stag handles, like the Buck BSA model, or ones that look like the Case knives, or wooden scales like a Mora or Opinel etc.
Or one that's idenfifiably Swiss Army like the Trekker is good too.
It's just as dumb as the looks of various rifles, but the AG Russel "funny folder" could be construed as a butterfly knife. (by a dunderhead, but this is who you're protecting your son from)
The look of the Agent's Office Knife is perfect, save for the fact it's double-edged. Someone in the troop or at camp will absolutely soil themselves once they figure that out.
You want to shield him from anyone who'll go bliss-ninny on him because they're accusing him of thought-crime for a knife that looks too modern or "tactical".
One possibility though is CRKT offers some of their M-16 line, but with blaze orange scales through REI. Might give the kid enough "evil tactical" look to make him happy, but the blaze-orange still says "tool" and takes away some of the "evil". (plus is high-viz to keep him from losing it, or another kid from appropriating it.)
http://www.rei.com/product/760507I think there's a drop-point one, the tanto isn't as useful to a general purpose woods/camping knife.