Lately, a string of kidnappings has cause the disappearence of many Jungle symbols from many Jungle Rares. Take this Snorlax for example...
Odd, ain't it?
Actually, during the last few print runs of Jungle (remember, Jungle is out of print), the Jungle symbol was accedently not printed on quite a number of Jungle rare sheets.
From a collectors point of view, this error isn't worth much more than a regular Jungle rare. It's still a cool error though.