NEW YORK/HONG KONG (Reuters) - State-owned Bank of China Ltd has offered yuan trading to its U.S. customers, a sign that Beijing this year may increasingly promote the use of the Chinese currency in major financial centers. An employee counts U.S. dollars next to yuan banknotes at a bank in Hefei, Anhui province in this September 21, 2010 file photograph. REUTERS/Stringer/Files The change at Bank