yep. the first letter should be an F, meaning it was made in Japan. Your 550 should have a 6-digit serial number, with the first digit telling you the year. 8 for 88, 9 for 89, 0 for 1990, 1 for 1991, etc.
look at the bottom of this page: http://www.jemsite.com/axes/htm_features/other.htm