There would have been a A-S A-M or a A-L stamp near the collar area.
This could have been printed in a small box but more that likely not.
TS uniforms came in 3 basic garment cut styles.
US cut for United States body type this will say US-S ect
Asian cut marked as stated above will have a small overall feel and could be considered Vietnamese cut hence Viet cut.
Then there are custom garments that follow no rules and can be marked in many different ways with tailor tags ect.
Your shirt is on the lower end of the price scale due to condition, size ,fade and last but not least pattern.
I hope this helps