The reliever played in all five games of the 2018 World Series and was the winning pitcher in Game 4.
The banner appeared in the upper deck of Dodger Stadium during the fifth inning on Sunday.
"The president said that?" the manager initially asked, apparently unaware of Trump's Twitter remarks.
The Red Sox took Game 1 of the World Series with an 8-4 win at Fenway Park.
The team notched a 5-1 win over the Los Angeles Dodgers on Wednesday night.
The aim is to bring regular season games across the Atlantic in 2019.
Chicago Cubs shake off the curse and advance to try to win their first World Series since 1908.
Murray is in Washington to receive the Mark Twain Prize for American Humor.
As the playoffs get underway, pitching talent is on display while the game's top hitters are just spectators.