illegibility

vaikealukuisuus The characteristic or quality of being illegible; the quality of being difficult or impossible to read.
1848, (w), w:Vanity Fair (novel)|Vanity Fair, Chapter 15,http://www.gutenberg.org/files/599/599-h/599-h.htm

“Poor thing! poor thing!” says Briggs (who was thinking of twenty-four years back, and that hectic young writing-master whose lock of yellow hair, and whose letters, beautiful in their illegibility, she cherished in her old desk upstairs).

I passed the time by adding to the illegibilities in my diary.

And on the back endpaper of the Collins Clear-Type Shakespeare, a work of fatiguing illegibility, he wrote the names in large letters, as though his succession had already been settled.

The illegibility of his handwriting made it unclear which answer he wrote.