American Express plans a public offering in Japan of 1 million shares of its common stock at $43.125 per share and has applied to list the shares on the Tokyo Stock Exchange . . . National Medical Enterprises increased its quarterly common stock dividend to 14 cents per share from 13 cents, payable Dec. 13 to shareholders of record Nov. 22 . . . Exxon said it increased its quarterly common stock dividend by 5 cents to 90 cents a share, payable Dec. 10 to shareholders of record Nov. 12 . . . Frank B. Hall & Co. will suspend payment of quarterly dividends on its common stock commencing with the dividend regularly paid in February, 1986.