Only two states, South Carolina and Nevada, require purchasers of ammonium nitrate fertilizer to produce identification. But the Fertilizer Institute, an industry trade group, has asked vendors to request ID voluntarily and to report any suspicious buyers to a hot line. TFI's pamphlet on the topic, titled "America's Security Begins With You," warns fertilizer salesmen to be wary of anyone paying with cash or who "avoids eye contact."