What are these markings on rear axle ?

[TollKeeper]

Where are their weld spots it’s all smooth metal lol if it truely is qc marks this truck went through a seriously QC check! These markings are through out the vehicle even under the dash

I can tell you from when I worked for GM back in 06-07, they would randomly pull a truck off the line and do a tip to tip QC inspection.. Maybe that was one of them.