Virtually all USCIS forms require a signature from the applicant. But what if that person is incapacitated or otherwise physically impaired so that the quality of penmanship is diminished? As long as the applicant is mentally competent to understand what he or she is signing, the document should be signed.
In this situation, it's acceptable for the applicant to sign with a simple line or mark that he or she considers a signature. Regardless of how bad it looks, the mark that the applicant considers a signature is enough legally. Alternatively, the individual can place a fingerprint in the signature space.
The person who is preparing the USCIS form on behalf of the applicant and witnesses the signature should include a cover letter that explains the applicant's limitations and reason for the poor penmanship.