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?
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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.