i note the skull & crossed bones of no. 4 were used long before pirates (and johnny depp
) as a sign of death, and is frequently found on grave stones and markers in catacombs. i will assume there is nothing piratical about your police force's use of the decoration since 1980. it is used by an assortment of modern military units to signify ferocity.
i note from wiki' skull and crossbones entry that:
The 2nd Lancers Regiment of the Portuguese Army also use the skull and crossbones as symbol and "Death or Glory" as motto, as the regiment was raised by a former colonel of the British 17th Lancers.