It was during his time as a trooper that Riggs conceived the idea of the “yield” sign, and he began developing it while attending Chicago’s Northwestern Traffic Institute in 1939.
He spent more than a decade experimenting with the sign, according to the Tulsa Police Department’s history book. His goal was a sign that would not only control traffic at an intersection but would also attach liability in a collision if one driver failed to yield.
The sign was a hit, especially among women.
...engineers in Dallas were pleasantly surprised by how grateful women were for the signs, the article said. Some women were apparently afraid to stop at night, so a yield sign helped them feel safe from roadside prowlers.
Until today, the only thing I knew about "yield" signs was that old joke with the punch line, "Of course I yield! I yield and yield, but they kept coming anyway!" Link -Thanks, Michael Mason!