Victor I just came across in my records the person who used the crest a demi-lion holding a sword.In my record on marriage grants I have a note
1st August 1784 Londonderry marriage grants;

David Caldwell confirms marriage settlement to wife Precilla ,crest only showing,a demi lion holding a sword with monogram D.C.

Now I have to find out who he is.
Plunkett Caldwell