In looking through all the books I have I cannot find it. But numerical countermarks were somewhat common usually used to denote the local currency value on a foriegn coin. In Central and South America there were a great many different numerical countermarks. They changed as often as the govt. did, and that was a lot.
Here is the Ebay listing for the coin: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270474431815 (Item 270474431815) A very rare example of my own collection.I believe this one is from Luzon Island or other South Asian countries".13" is not a good number in China and Westen countries,so in China,we have no "13"chopmarks known.The well known is 8,and then,11 & 5.I prefer this one is a counterstamp,but I have no idea about where it used. Seller is located in Shanghai, China. That should tell us something.
Yes, I've been in contact with the seller having purchased some of his other chopmarked coins, but he too is in the dark over this counterstamp.
