Unexpected treasures found among items grandma saved are not uncommon. Think before you clean out old paper ephemera. In May, Swan Galleries is auctioning 22 posters made in the 1930s by WPA artists to encourage children to read books. The modernist posters are estimated to bring about $7,800 as a group. (They are being sold in 5 lots.) How lucky no one dumped them when cleaning a public library attic.