I've always used the "not equal to" sign:
John SMITH ≠ Mary JONES
K.
Yes, I would read that as John SMITH is not married to Mary JONES (and their children are on the generational line below). BUT as far as I am aware, there's NO well recognised ISO standard for family history (tree charts, or otherwise), so if you simply put your own "key" list of your chosen symbols on your document or at the introduction/cover sheet, I would hope anyone reading it would appreciate your hand prepared document. That is definitely a labour of love task you have set yourself.
Cheers, JM
Since (for me at least) the research is (and always will be) ongoing, I would never put
lots of labour into a graphic representation.
Drawing fancy diagrams of trees is what computers are for.
BugBear