“Across Milk St. from the Post Office Building where Dr. Benjamin Spock’s case is being heard stands a sign that reads in large green letters: ‘Boston Five.’ A second look reveals smaller letters that complete the title of a branch office of The Boston Five Cents Savings Bank. But the anonymous adman who decided to capitalize those two particular words inadvertantly provided a sort of marquee for the drama of the so-called Boston Five and their fight against government prosecution for illegally counseling draft resistance. Inside the Post Office, in an austerely decorated twelfth-story courtroom, the adversaries in the case gathered last week for the first encounter in what may be a long legal duel. The five defendants–Spock, Yale Chaplain William Sloan Coffin, Harvard graduate student Michael K. Ferber, writer Mitchell Goodman, and former National Security Council staffer Marcus Raskin–were all there, each with one or more attorneys. So were…