you can get a "employment verification" letter (sample at: http://www.path2usa.com/employment-verification-letter-for-us-v or "termination letter" from the company to prove that you worked for a company from mm/dd/yyyy/ to /m/d/y. most company probably don't have the stamp like the one in China, but in this country company typically print it on company letterhead http://en.wikipedia.org/wiki/Letterhead paper and hr signature to make it formal