In a case in which uncle sam uses work clothes he is inviting the public to join the labor force because it is a priority to be satisfied.
Explanation:
Two main reasons back to this answer. First of all, Uncle Sam is a military Icon that has been associated with the phrase "I want you" or in other words, "I need you". In the war he was used as a tool to motivate people to fight for their country in different roles. In this case he motivates them to join the workforce, an example of this is the yellow girls. They were famous for helping make missiles during the war and ended up yellow as a cause of the phosphorus.
