Many IMG in china, Russia, Ukraine face 186 rejection because of signature mismatch so you need to guide your university.
Here is ECFMG reply.
If your medical school would like to update their authorized signature list in our records,*ECFMG® will accept an original letter from the school that includes the names, titles, and sample signatures of those officials that the school has deemed as authorized to sign applications and to verify the authenticity of credentials.* This letter must be on the school’s letterhead, must be signed by the Dean, Vice Dean, or Registrar, (or the equivalent positions at your medical school: example: Rector, Vice Rector, Principal) and must include a sample of the medical school seal.* ECFMG must receive this letter by mail to confirm that it was posted from the medical school.* We cannot accept this letter by fax.* This letter can be mailed to my attention at the following address:
3624 Market Street
Philadelphia, PA 19104