Ownership of an auto knife is a state issue. When I lived in Missouri, it was perfectly legal to own (not carry) an auto knife if you were either law enforcement or a "collector". Good thing I was a "collector" ;-). Nope, didn't need any type of registration to be a "collector", just had to tell the knife shop that you were a "collector". :-) Don't ask me, it's just the way the law's written....
Course now that I live in Illinois, I don't own or carry any autos. Only owned 1 in Missouri and got rid of it - it was useless for me anyway like the ubiquitous "boot dagger". They are completely illegal here except for LEOs and EMTs (they let the EMTs carry them for cutting seat belts in emergencies - makes sense).
Oh yeah - see the last argument between Joel and I. The only thing we could agree on was that 420 sucked. :-)
Tim