The former angel Anna Milton began using a sketchbook to draw pictures after she began hearing angels talking. She drew pictures of the seals that had been broken by Lilith, such as the Raising of the Witnesses and the arrival of Samhain, and even drew the round, stained glass window of her father's church.
Anna used this sketchbook during her time in Connor Beverly Behavioral Medicine Center. After she escaped, her psychologist saw the drawings but considered them to be merely the result of Anna's delusions. The woman later handed the sketchbook to Sam and Dean.
After the brothers went to Anna's house in search of her, Sam recognized a stained glass window in one of the photographs and compared it to the one Anna drew. This led Sam and Dean to Richard Milton's church, where they finally found Anna.
What became of the sketchbook after this is unknown, however, some of the pages were removed from the actual sketchbook after Sam and Dean left the Medicine Center.