Okay, this would be invaluable for maps, trails, and paintings. With this, players could make their own paintings and share them (When MPS comes out). They could also keep them in their inventory and look at them from time to time, if it's a map. They could also be put on walls like paintings, or, be stuck in the ground like large signs.
They would take up 3x3 blocks, and probably the best application would be making huge wall maps.
They could be edited by other players, and they could be crafted any way to make larger and larger drawing boards.
= drawing board
[iron] = air
This would make a large place-able Y-shaped sign/painting, depending on which kind of drawing board was used to make it.