The plaque reads: "In memory of Boatswain's Mate William H. Cashman, Surfman Frank W. Griswold, Surfman Edward P. Stark, who of Station No. 31 United States Coast Guard lost their lives in the performance of their duty, March 10, 1928, when the Steamship Robert E. Lee stranded on the Mary Ann Rocks Southeast of this station. Greater love hath no man than this, that a man lay down his life for his friends."
Source and more info: https://en.wikipedia.org/wiki/Coast_Guard_Station_Manomet_Point