Los Angeles City Atty. James K. Hahn has issued a public warning about peddlers who may be passing off cheap costume jewelry as gold in the downtown area. The warning follows two separate convictions of people for selling fake gold jewelry. One peddler, Lena Maria Arias, 29, of Monrovia, was sentenced to 45 days in jail for selling fake jewelry to Crocker Bank Building office workers; the other, Gabriel Jose Garcia, 29, of the Sawtelle district, got 60 days for trying to sell a phony gold watch and bracelet to a plainclothes police detective on a lunch break across from City Hall. The con artists are sophisticated, Hahn said, and the jewelry is stamped with authentic-looking "14K" and "18K" marks.