We had a similar post some time back and the consensus was to return it to the family of the owner. I believe there is a government agency which assists in that endeavor. I recommend it. Hopefully younger, remembering minds will chime in.
They should be sent to the Pentagon exactly as pointed out here, the details are important because they could belong to a POW-MIA, they should not be kept under any circumstances IMHO...
If you do decide to send it in, lie about where you found it. The last thing you need is a bunch of government agents on your doorstep looking to rip your dump apart to look for more dog tags!