A "police number" is a chassis number issued by the police when the original can't be used for some reason, or in official speak: "Motor vehicles with missing, suspect, altered or damaged identification particulars"
For older vehicles they typically start with the first letter of the issuing state (N = NSW, V = Victoria, etc.), then the first two numbers are the year it was issued, and they end with a "P" (for Police presumably)
There is a thread around here somewhere...
http://www.gmh-toran...hassis-numbers/