Letter scraps are little text fragments about the mystery of Leonora Johnson. In GTA V, there’s a totla of 50 letter scraps, dispersed over the whole map…
You recognize those letters by a glowing, white pece of paper, that you can find on the ground or on objects. When you get closer by the paper you can hear the sound of paper floating into the wind.
After finding the 50 pieces, the letter will be avaible to read and a new mission will unlock.