Illegible (adjective)

1. Not able to be read or deciphered due to poor or untidy handwriting or printing.
2. Not able to be understood or interpreted due to being unclear or ambiguous.

Origin:

From "illegible" meaning not able to be read or understood.

Examples:

1. The document was nearly illegible due to the poor handwriting.
2. The signature on the check was illegible and could not be verified.
3. The instructions were printed in an illegible font and were difficult to read.
4. The message was illegible and couldn't be decoded.
5. The text was illegible, it was hard to understand.