NecronCell is correct in his citation of pg 7 of the BRB, "Zero-Level Characteristics."
I suppose an AP "0" weapon is the exact opposite of AP "-", though I know of no weapon that posesses such a characteristic.
The point I was trying to express is that vehicles, other than walkers, do not have stats in those categories, and as such they could put anything they like in there, like a !, or a $, or a R, or an "O" as in Omit... though I had posted a Zero.
The Characteristics that non-walker vehicles possess can be found in the 40k RB, pg 56, left hand side.
The "Additional Characteristics" that walkers possess can be found in the 40k RB, pg 72, left hand side.