The 1971 MUTCD was published by the Federal Highway Administration. This replaced the 1961 edition, and served as the official edition of the MUTCD in the United States until the publication of the 1978 edition.
Notable Changes from the 1961 Edition
Yield Sign (Section 2B-7)
The yield sign was changed once again. It changed to what we know today, which has a "red border band and a white interior and the word YIELD in red inside the border band."