i love the fact that the first century BCE Tironian et still shows up in irish gaelic signs today. [1] the shady characters blog has a great write up on Cicero and his scribe Tiro [2]

[1] http://www.shadycharacters.co.uk/2011/06/the-ampersand-part-... [2] http://www.shadycharacters.co.uk/2011/06/the-ampersand-part-...

Interesting! In the first page linked, the tironian ⁊ on the page from the Belgian Bible looks like it could have been the precursor for the "+" sign.

Perhaps the marginalia in French are written in the Roman alphabet, and the other script is Latin written in the Tironian alphabet?

I definitely think that you are on the right track! (Read my other comment.)