Signaling a turn is required under NJ's traffic statutes, and there is no provision allowing for failure to signal if no other traffic is around. Simply, this means that while it would be very unlikely that you'd be stopped, much less summoned, for failure to signal alone....it could happen. Why take the risk?
As others have mentioned, it's best to 'get in the habit.' Humans learn reflex actions by repetition, sometimes referred to as "muscle memory." This is the force, which causes you to be able to type without looking at your keyboard, dial a phone without concentrating on the next digit, and which sometimes drives us to stomp the brake pedal, even though we're in the passenger side of the vehicle.
By signaling every turn, you'll never have to worry about forgetting to signal a turn, in which other traffic may be affect. You also won't have to worry about getting that very unlikely summons.
That said, there is case law, in which it was argued that there was no other traffic in the vicinity for the driver's turn to potentially affect. The case was upheld, based on the fact that the officer's vehicle may have been affected by the turn.
http://www.romingerlegal.com/new_jersey/appellate/a3783-04.opn.html
It's a bit confusing to read, but leaves one with the impression that, in the right circumstances, a driver could get away with being caught failing to signal, but that it's highly unlikely. If you're stopped, even if there's no other traffic on the road, the chances are that the officer's patrol vehicle will be all the "other traffic" they need for a conviction.
see NJS 39:4-126 for the entire Appropriate Signals statute.
I'd just signal. It's worlds easier.