Griffonage
Scribble. Illegible handwriting.

This is an affliction with which I have, according to my father, been blessed from the earliest age — my handwriting always did look like an arthritic spider had crawled out of the inkpot and it is still getting worse!
The derivation is from the French griffonage, griffonner, to write badly or scrawl. The OED records the first documented usage as 1832.