Let's see...
There are 12 signs and 7 billion people on Earth.
One of those 12 occupies my Ascendant, your Ascendant, his and her Ascendant.
Here we go again.
How can the Ascendant, taken alone, specify someone's handwriting?
I am not a graphologist. But my scanty understanding of graphology leads me to believe that a person's handwriting, like their fingerprint, is unique to them.
My scanty understanding also leads me to believe that a person's handwriting is an expression of their whole, or composite, personality. Seems to me this would implicate the entire chart in any analysis of handwriting.
Transits and directions would also be involved. I once saw a graphologist's analysis of Hitler's handwriting, and it was pointed out that the handwriting changed over time and ultimately showed Hitler "heading for a great fall"...toward the end of his life, the end of his signature ran downward and then dropped off.
Can I assume, as I think an expert graphologist might, that small and illegible handwriting, with large spaces between words (they are disconnected) might indicate a personality with cramped and disconnected thought patterns? Does sloppy handwriting indicate sloppy thinking?
Mercury rules "written communication." Of course, we need to know Mercury's sign and house position, his aspects, his motions.... And then there is the Moon, and a gang of other planets to consider.
As for me, if I want to talk to you, I'll just call you up and text you. That way you can't decipher my strange personality.
And there will be no need for an astrologer to figure out how I sign my name. Just as well; they probably have better things to do.