For Americans, I wrote: "may require returning to the US".
Here is why:
U.S. DEPARTMENT OF STATE travel.state.gov/travel/tips/emergencies/emergencies_1201.html
"Go to your local police department where you reside or last resided in the United States, request that the police conduct a local or state criminal records search and provide you with a document reflecting that there is no history of a criminal record. Local police departments may require your personal appearance in order to conduct the search."
The FBI www.fbi.gov/about-us/cjis/criminal-history-summary-checks
"The U.S. Department of Justice Order 556-73 establishes rules and regulations for the subject of a Criminal History Summary to obtain a copy of his or her own record for review. The FBI's Criminal Justice Information Services (CJIS) Division processes these requests.
Who May Request a Copy of a Criminal History Summary (or Proof That a Criminal History Summary Does Not Exist)
Only you can request a copy of your own Criminal History Summary."
I guess you can try having your high school bud, your Mom, or ex-wife try to get what ever you need from the police. Once whoever gets the certificate, it needs to be translated by an "official translation company." And finally, the certificate of no criminal conviction must be authenticated by a Chinese Consulate. Note; not an Embassy but a Consulate. Usually there is a consulate office within each embassy but there may be several consulates in a country.
So, while someone may lack imagination, the awful reality comes when your high school bud, your Mom, or ex-wife, steps up to the counter at your local police station and finds he/she will not be allowed to get your information.
Interestingly, here
lawandborder.com/?p=2565#more-2565
says "The certificate should show that the applicant has no criminal conviction from age 18 to the present. There is no provision for whether an applicant needs to present an additional certificate from a third country where he or she has previously resided."
This the only mention of "from age 18" I could find.
Another possibility is the FBI "Criminal History Summary (or Proof That a Criminal History Summary Does Not Exist)" Which may be possible to get by mail. I have heard two stories about the FBI check; 1) it took about 6 months to get while in the US, and, 2) there was a problem providing required fingerprints when outside the US.