The NMR says:

"Stone with natural markings. Not an antiquity"

http://www.pastscape.org/hob.asp?hob_no=228449&source=textonly&period1=None&county1=Wiltshire&class1=None&hob_name1=The%20Kinward%20(Or%20Kenward)%20Ston

I'm not criticising jimit's posting of this stone, just passing on some info. I'll have to go and have a look at it.

baz