Why do people pin money to themselves on birthday?

Answer 1

From what I've read it seems to be a tradition amongst black people that may have started in Nigeria and spread during the mass interbreeding of the tribes during the years America was involved in slavery.

People that know about the tradition pin money (or donate money to be pinned, if squeamish about being near a woman's bosom) to people's shirts on their birthday.

If traveling to a highly black-concentrated area, such as the American South, Detroit, or the like, it may be quite advantageous to pin a dollar to your shirt and watch the money roll in as strangers wish you many happy returns.