This letter to MT's daughter Clara Clemens Gabrilowitsch dates from the last months of his life. He is writing from Bermuda, where he had gone in search of better health. The letter contains some extraordinary sentences about Isabel Lyon, whom he had just fired after many years as his secretary. When MT wrote his daughters he usually signed himself "Papa" (especially when he wrote Susy) or "Father." But there are several other published letters to Clara signed "Marcus." I'm not aware that he ever signed letters to anyone else with the name.
At this time Clara was traveling in Europe. The envelope which MT addressed to Berlin is also accessible below: I think it adds to the pathos of MT's loss of his family to note how many cities it had to travel through, including Monte Carlo and Rome, before it caught up with his one living child (Susy died in 1896; Jean, just 10 weeks before this letter was written -- the black border around page one of the letter is for her death).TRANSCRIPT OF NOTE