Thanks to everyone, and to Susanne and Larry STI for immediate answers. Hurtig hjælp er dobbelt hjælp!
I chose lozenge because it could also be used in more literal senses, as it was not 100% clear what the client meant, and they did not answer.
Both lozenge and diamond exist in typography - the lozenge is said to have become widespread in England with the printing of the Book of Common Prayer.
The lozenge is an outline figure, while the diamond is solid.
http://www.hypotext.de/unicode/index.php?chapter=tables&colu...
I have to admit that I still haven't found the pastille in Danish, but I think I have seen it in print somewhere - I'll keep searching!
(I worked for a while as a proof reader at a printer's many years ago...)
And as a child was given blackcurrant pastilles if I had a sore throat, or Rowntree's Fruit Pastilles when I deserved them... Those were the days :-)