What does illegible?

Sometimes. The writer can do something simple or disguise i guess you can say, their work. The most illegible graff is probably a wildstyle because the writer just goes all out on those.

The word 'illegible' means (of handwriting, print, etc.) not legible

unreadable;not able to read

I L L E G I B L E bill, bell, gill, ill, eel, big, leg,

The teacher refused to grade the illegible scribblings on the paper.