Rating the sprint during retrospective

I am new at this company and within this company the DT and PO have to rate the sprint with a number from 0-10. I was not used to this at my former job and employer. At my former employer i joined (as PO) a team who gave smileys (happy, unhappy, frustated etc.) to a sprint. But not an official rating. What are the guidelines according to scrum according rating a sprint?

Posted By - Aida de