Q: A postscript may be a sentence, a paragraph, or occasionally many paragraphs added, often hastily and incidentally, after the signature of a letter or (sometimes) the main body of an essay or book. In a book or essay, a more carefully composed addition (e.g., for a second edition) is called an afterword. The word "postscript" has, poetically, been used to refer to any sort of addendum to some main work, even if it is not attached to a main work, as in Sren Kierkegaard's book titled Concluding Unscientific Postscript.

Answer this question: where is p.s. written in a letter?
A: after the signature
Explain how we arrive at this answer:
Explanation: To answer the above question, the relevant sentence is: A postscript may be a sentence, a paragraph, or occasionally many paragraphs added, often hastily and incidentally, after the signature of a letter or (sometimes) the main body of an essay or book.