A few points.
1) IMHO for what it's worth, the sign was trying to convey the message that racism exists in America, and it's as traditional as baseball. Unfortunately - the verbiage left enough ambiguity to spark debate and misunderstanding -- AND -- Fenway Park , in the middle of a game, isn't the place to launch such debates. They got on TV ("Look Ma, I'm a STAR!")...
2)
Yawkey Way? Yeah, I'd have no problem with renaming it - keeping in mind that various facilities built by the Yawkey Foundation - there's a student lounge/center near Kenmore Square with the Yawkey name, also a Boston College athletic facility - these were built with the Yawkey Foundation endowment. And THOSE, I have no problem with them retaining the name. Just one thing - don't give renamed Yawkey Way a commercial tie-in. "Samuel Adams Way", anyone????. NO. And let's skip over Dapper O'Neill and Louise Day Hicks while we're at it.
3)
Earl Wilson. Ah - some say the worst trade in the latter half of the 20th century was the Bagwell-for-Anderson swap. I disagree. Trading Earl Wilson to Detroit for Don Demeter (you may have to look him up) was the most devastating. Had Wilson been winning games for the Sox and not Detroit, the Sox might have clinched the '67 pennant a few days earlier, they would have entered the 1967 WS with a rested Jim Lonborg in game 1, and the results would have been different with Wilson going in game 2 or 3. And they would have had more of a shot in 1968, Lonnie's knee operation not withstanding.
4)
Integration in Boston Sports. While the Yawkey/Red Sox situation was deplorable, we also cannot forget the progressive attitude of the other four sports teams - Braves, Patriots, Bruins, and particularly, the Boston Celtics.
Walter Brown, historically, did not get the credit he deserved. He went out on a limb to draft the first African-American NBA player. It should be noted that the BAA (NBA) had a competing league when it started in 1946 - that league was the National Basketball League; it had superior talent to the BAA, and had African-American players in it at various times. According to Len Koppett's Silver Anniversary NBA book, Brown raised hell in the draft session by selecting Cooper. But he stood firm.
Braves? 1950, Jethroe, already mentioned. Patriots? They had Rommie Loudd as one of their coaches, IIRC that was pioneering, and is oft-forgotten. Bruins? O'Ree. There weren't too many blacks playing hockey - but they DID bring him up.
Regarding Rommie Loudd - obit from the New York Times, 1998
http://www.nytimes.com/1998/05/18/sports/rommie-loudd-64-pro-football-coach.html