Disklavier

With so many insightful and helpful people here I thought this board 
would be a place I might get this question answered.
I remember when I was very young I had a long piece of cardboard that 
fit behind the keys of the piano naming the keys. I'm looking for that 
same thing now but can't find one on eBay. I don't know what to call 
it. I may have found one and I did purchase it but still not sure and 
really doubtful it's what I'm looking for. In any case I still need 
one more. I've looked at so many piano sites but can't find it. Is 
there a name for these things? Can anyone direct me? Thank you, Jeff