Chris you may be thinking of a requirement by the AISC for each weld to be identifed with the welder who produced it up to the point that the weld is inspected and signed off for final inspection. A stamp is one of many ways of accomplishing this..
D1.1 does require that the inspector identify the welds that he/she inspected...See paragraph 6.5.4
edit: nevermind...I see others have already stated the same thing....