<VV> piston question along with wire wheel update

[judynrandy at comcast.net]

Since i'm doing a reseal on the 21,000 mile engine in this '64, I decided to pull the pistons out of the jugs to make it easiser to deflash the jugs and to ensure the oil control rings were all loose and working correctly. Don't ask how I know to check that. : - )  As I was cleaning the carbon off the piston tops, I noticed 3 of the 6 had the number "10" stamped on the top of the piston.  What does it mean  and why is it there? 
As for the wire wheel thing, thanks to all who responded.  I'm now in the market for a good "dead blow" hammer.  Also, these wire wheels are the real deal.  The knock offs have the off stamping along with the arrow.  And they all match correctly.  They have a Chevy emblem in the middle, too.  Plus the dude also has a spare tire mount in the car for said wire wheels. Again, these are perfect and look brand new!!! 
  
Randy (Cap'n) Hook 
Hopewell, PA