Dashes and Dots Under Spy vs. Spy
That series of dashes and dots is Morse Code for "By Prohias".
Antonio Prohias was the creator of Spy vs. Spy first seen in the January 1961 issue of Mad #60.
Mad hired him after he fled Castro's Cuba to America.
He had been quite the sensation in Cuba, having won many awards for his illustrations.
Mad couldn't resist.
He continued to draw Spy vs. Spy for nearly 30 years until retirement in 1990 due to illness.
Other Mad contributers carried on where he left off until
Peter Kuper became the main man up to the present day.
All the while that code has been lurking beneath the Spy vs. Spy title in honor of the master spy, Antonio.
Prohias passed away February 24, 1998.