My handwriting has never been terrible. I don't write in cursive anymore, but when I did, it was OK. My manuscript varies considerably, depending on what I'm writing. When filling out official documents, obviously, I try to keep it formulaic and neat. When writing casually, certain letters or words morph into half-cursive loops, odd shapes/sizes, tiny illustrations... almost freeform expression, like the conventions of handwriting have gotten kind of drunk... My signature is doctor-style barely legible, and in some instances, I reduce it to an iconic symbol that I've invented, consisting of my first and last initial.
A curious point to this is that I've never held writing utensils the "RIGHT" way. When I was in grade-school, I had teachers gently correct, then scold, then seek remediation for this behavior. I remember having these plastic finger-placement thingies stuck onto my pencils, so that I had to hold the pencil like it showed me to. Thumb here, index finger here, etc....
I just took them off. It always felt WRONG to write the way that they showed me to. Other kids would puzzle over how on earth I could hold a pencil the way that I did, and mockingly tried to do it themselves. Whatever. It worked for me. Still does
Whether or not any of this has to do with Asperger's.... it might. Who knows??