If you're looking like you belong there, nobody will bother you. Start digging holes, either beach or grass, and not fill them in, then you stick out like a sore thumb. Someone might challenge you and ask for your permit. Most of the time they ask if you had any luck. it's just a way for the municipality to make a buck. Nobody cares if you have a permit.
However, that one day you do not have a permit and they suddenly decide to start checking permits, now you have a problem. They might just ask you to stop or they might issue you a summons.
With the money being pumped into fixing up Jones Beach and the state parks, you can expect to see more pencil pushers out observing what's happening and that's when bad things start to happen to md'ers.
Don't have a permit, metal detect at your own risk.