Hi Glasswizard,
This design is called Ovalis, apparantly originally designed 1958. There are several different sizes see
here.
I think this style of mark indicates a fairly recent production. The current issues of the Aalto 'Savoy' vase have a similar mark and the Ovalis design is still listed on the Iittala website. There may be more information about dating the mark in the
Designlasin book that Max and Adam have.