How do you add a postscript to a letter?

After you sign a letter, you can add a postcript by writing "P.S." underneath the signature, then writing your message to the right of the abbreviation. (Postscripts are not recommended for official or business letters, only friendly letters.)

Example:

"...Write back soon!

Your Pal,

John

P.S. I forgot to ask - how's Aunt Margie doing? Any news from the doctor yet?"