From a legal perspective, Sir Galant is almost certainly correct. But it
may be a
"gravity knife" which is also illegal in most states.
From a
practical perspective a "switchblade" or a "gravity knife" is whatever the officer handling your SOG Arc-Lock thinks it is. Let's suppose someone down at the station showed him the following YouTube Videos of the Arc-Lock in action:
Video 1
Video 2
Now put yourself in the officer's place. What is he likely to think of an Arc-Lock knife?
This isn't a concern unique to SOG, either. You'll run into the exact same problem with Spyderco, Kershaw, and Benchmade knives. All these brands have a bunch of models which can be "flicked" open instantly with one hand. My suggestion is buy the SOG Mini-X Ray, it's a great little knife, just be cautious how you open it in public.
Over 20 years ago, Jeff Imada gave some very good advice about fast opening knives in his
Balisong Manual. He was discussing butterfly knives, but it's just as true today for the SOG Arc-Lock: when in doubt, open the knife slowly
and with both hands.