CREDENTIAL: The American Sign Language (ASL) sign for "credential / credentials"

If you mean "CREDENTIAL" related to "digital technology" (information that identifies an account and keeps it secure- username and password) you can sign 'username and password'
 

If you mean "CREDENTIAL" as in "evidence of authority, status, rights, entitlement to privileges usually in written form" or "provides basis for confidence, belief and credit" you can fingerspell, or sign PROOF / EVIDENCE, REFER / REFERENCE or REPUTATION

Often when someone is asking about your 'CREDENTIALS' they want to know about your degree, knowledge, reputation, experience, and skills. More than just the paperwork.

PROOF / EVIDENCE:

REFER / REFERENCE:

REPUTATION:

Notes: 
See: DIPLOMA

KNOW

EXPERIENCE

SKILL