Letter "P" marking on LS 430 spark plug tip? What's it mean?
 

I recently bought a 2006 LS 430 and was considering changing the spark plugs (although the car is running wonderfully at 128K miles). I took one out to examine its condition and saw the letter "P" marked on the tip of the plug that is connected to the coil pack boot when installed. On the LS 430 forum, a member suggested the "P" marking is a clue that it is a factory-installed original plug. Can anyone confirm if that's correct? Or otherwise explain what that marking means?

FWIW, the plug is a DENSO SK20R11 iridium. I assumed (perhaps wrongly) that the "P" stood for "platinum". Even if that's correct, is it possible that only the factory originals are marked with the "P" (perhaps to ensure the proper plugs are selected/installed)? Searching online, I have definitely seen the same DENSO SK20R11 iridium plugs offered for sale *without* the "P" marking on the tip.

I'd greatly appreciate any information you might have!