Shimano added the word 'Ultegra' to their 600 group set in 1988 with the introduction of the 6400 series groupset.  Also often recognized by the tri-color stripe on many of the parts. 

The Ultegra group was developed to provide a high-performance racing type bicycle for amateur racers and performance oriented sports cyclists. Ultegra features polished bearing races, high strength steels, a striking modern colour treatment and compact high-tech design theme. This approach creates a new upgraded image for a fashionable high quality racing-type bicycle aimed at the performance cycling enthusiast. (1991 Dealer Manual)