What exactly is a Pencil Board?
Pencil boards (Shitajiki), are used to place under a sheet of paper (or a pad) such that writing on the paper won't indent the sheets underneath. The wiki page for Shitajiki says:


  Merchandised shitajiki are very common, featuring images of everything from tourist attractions to celebrities to anime and manga characters. Most shitajiki designs only go through one print run, making them very collectible and often difficult to acquire. Collecting shitajiki is a hobby for many anime and manga enthusiasts. As collectibles, shitajiki are also often used for decorating or other ornamental purposes.