In all my years of collecting I have never seen this mark before and I couldn't resist, even though I was paying a premium.
This is from the late 1950s or 1960s when the backstamp was often in itself a little work of art. But it brings us to the question - when you're buying, how much is too much? Blunt answer: it's worth what you are prepared to pay. Look on TradeMe, check second hand shops, then make up your own mind. If you want it by all means buy it, regardless of price. Just don't expect to make a profit in a hurry. (Then again, I am amazed at how much prices have gone up since I wrote my book in 2006.)
The flipside of paying too much is paying too little. I found this bowl in a charity shop in Tauranga for $5. It was made by Crown Lynn (then Ambrico) for the American army in the early 1940s and it's worth $50 or so, even though it has a glazing fault (which you can't see in this photo). The nice shop lady carefully pointed out the fault before she sold it to me. Should I, in return, have pointed out the bowl's significance and given her another $20 or more? I didn't.
FYI, this is what the base looks like. The bowl is about 15 cm wide.