This may be the abbreviation of "Jewelry and Jade Appraisal Research Center of Yanshan University", a private appraisal institution. The address is No.438, West Section of Hebei Street, Qinhuangdao City, Hebei Province. The number of enterprises is very small, the area is very small, and there is basically no authority at all. However, it is generally stipulated that the full name of the certificate seal should be used, so if the seal is "Yanda ...", it may be a false certificate.