Br knuckle belt buckle, a third degree weapons charge?

ive owned a br knuckle belt buckle that i have had for about 3 years now. I have been through atleast 4 tsa chackpoints in seattle, newark, and tampa are ports. they all asked me if it was a belt buckle, took a note of it and then released me to my plane. recently i was coming back to tampa from newark. it was on my carry on, along with my belt, and i put it in the front pouch so they didnt think i was trying to hide it. i got arrested, and slapped with a 3rd degree weapons charge. i have the package that i bought it in, the location of the store, and it says "BELT BUCKLE" in bolt print. i have never had any trouble with the law before, and i honestly dont want this on my record. is my case win-able? what would be my maximum punishment? i honestly didnt know they were illegal. i figured if i could legally buy them, then i could legally use it as intended. i had no cruel intent and have no violent past.