hello Anne - is your mark the same as on my vase in this link....... http://www.glassmessages.com/index.php/topic,43603.msg243391.html#msg243391
...... sort of old English script with the word a little curved.
As you will see on page two, Frank was able to assist with a positive attribution from a complete 1970's Waterford catalogue, which would assume he still has.
Understand from Nigel's joint publication with Jeanette Hayhurst - 'Art Deco To Post Modernism - A Legacy of British Art Deco Glass', that in the late 1990's Waterford introduced a modernist range of styles designed by John Rocha - obviously unlike traditional Waterford patterns that most people know. In the event, my vase is shown in this publication, although at the time I didn't have a copy.
Your decanter might be from the 60's - 70's period like mine, or perhaps later - it certainly looks a more contemporary and restrained non-traditional design. Certainly post 1960, and perhaps a lot more recent.
Perhaps we might persuade Frank or Nigel to comment.