The PI or his or her designee signs and witnesses the participant's written agreement. In the proper ethical and legal framework of informed consent, the protocol consent document is an educational supplement to the personal discussions between investigator and participant.
What are credentials? Credentials often refer to academic or educational qualifications, such as degrees or diplomas that you have completed or partially-completed. Credentials can also refer to occupational qualifications, such as professional certificates or work experience.
In other states it might be called a license or a certification. A credential is the permit your state issues after it confirms that you've met the necessary requirements. A credential is only issued to individuals who have met all the state's requirements.