Cost, who´s real name is Adam Cole, according to Wikipedia (wikipedia), often uses stencils, which are usually cut out pieces of paper or cardboard (wikipedia). They get glued on walls, doors, walk/don't walk street-crossing and other places with the help of wheat paste, a gel or liquid adhesive made from wheat flour or starch and water .
Now Cost is back! His messages are again amassed in the streets of Soho and Lower East Side like Lafayette, Green or Mercer Street. And he is transforming his popularity into money. VillageVoice reports that he is selling parts of his work in posh galleries and that some collectors pay more than $30.000 for pieces of Cost (villagevoice).