The first stop signs originated in Michigan in 1915 and featured black lettering on a white background square sign. In order to reduce confusion and provide a standard, the octagon sign shape was adopted in 1922. In 1924 the colour of the signs evolved to black lettering on a yellow background. This remained the standard until 1954 when it changed to the white lettering and red background we know today.
Many countries around the world have adopted parts of this standard, but typically feature the translated version of the word stop. Reference: http://www.myparkingsign.com/MPS/article_history-of-stop-sign.aspx