187 is the American police code for a homocide (a kill).
Obviously 666 is the number of the beast however, I don't no that The Haunted associate them selves so readily with Satan or the occult.
In any case if that is the reason for the appearance of the characters "6" 6" 6", I have no explination for the 0 and the space bewteen the last two 6's. Perhaps simply "187 666" was just a little to obvious.