Do you mean this mark: "For Law Enforcement/Government use only"?
If that's what's on it, it means nothing anymore. That inscription means that the lower was assembled into a rifle of LE/Gov configuration (flash suppressor, bayonet lug) during the Kiltoon AWB years. The AWB is gone, so the inscrition is meaningless.
However, if the lower is made by Colt or FN and says "U.S. property", then you might be looking a a problem.
Some other companies (who are not suppliers of complete rifles to the military) put "US rifle", "US property", "Government Model", etc on their rifles either because the rifle they are selling is identical to something they supply to a .fed LE agency (like the Rock River DEA carbine) or just to be cool.
The long and short of it is that anything is legal to own as long as it hasn't been stolen from a .gov armory.
I have a rifle marked "U.S. Rifle, M1", which made it .gov property at some point in the past. Fortunately for me, that rifle has been surplused so it was legal for me to buy.