"Chicken scratch" is a phrase that refers to messy, illegible handwriting or drawings that resemble the chaotic scratches of a chicken. It means something that is difficult or impossible to read or understand due to its poor quality. Full definition
My disclaimer is that if you're notorious for chicken scratch writing, you might need to either write much more purposefully or perhaps not invest. (businessinsider.com)
Don't worry if they look like chicken scratch! (theeverygirl.com)
My memory of that first day, mostly a blur now, is of the smell of manure and the flock of chickens scratching for corn around the entranceway. (sciencemag.org)