B'siyata D'shmaya or Baruch Hashem
What is the origin of putting BS"D (or Beis Samach Daled) on the top right hand corner of anything one write?
BS"D stands for b'siyata dishemaya and B"H stand for B'Ezrat Hashem, which mean "With God's help in Aramaic and Hebrew respectively."
People do this as a way to always remember that anything that they do could not be done without the help of Hashem.
According to this answer to a different question:
If Rambam is indeed the first Jewish source of this practice, it would likely indicate that it could be the result of influence from Muslims who have a similar practice of writing "B'smillah ilrahman ilrahim" (In the name of Allah the most merciful) on their written documents.