Does anyone know what this kind of writing board is called?

Hello everyone. My mother is extremely hard of hearing, and having to shout answers to her questions over and over again (because of her loss of short-term memory) is about to drive me crazy. I recall that some years ago there was a type of board that children and others used that had a dark slab with a cellophane-like grayish plastic sheet over it, and if one wrote on the sheet using a non-leaded pencil, the written areas would stick to the slab, making the letters appear black against the otherwise gray background; the writing was "erased" by pulling up the sheet so that it no longer adhered to the slab. This would be perfect for communicating with my mother, but I haven't seen one in a long time and I can't remember what they were called. Does anything know what they're called? I hope they still exist. Thanks, Bob.