It’s pretty simple, and there are two ways to do it. Note that in Chinese letters, you can stick the P.S. anywhere on the page, although the lower-left corner is normal as in English letters.
The quickest way is just to write 另： and then your extra message.
- 另：我很想念你。 (Lìng: Wǒ hěn xiǎngniàn nǐ.): “P.S. I really miss you.”
- 另：我爱你！ (Lìng: Wǒ ài nǐ!): “P.S. I love you!”
Alternatively, you can use 又及. Brownie points to MDBG for having this listed under “P.S.". Nciku hints at it in an example sentence but doesn’t give a full explanation.
- 又及：还有一件事… (Yòují: hái yǒu yí jiàn shì…): “P.S. One more thing…”
What Nciku and other sites _do _have are a few Chinese words for postscripts themselves, such as:
- 附言 (fùyán): postscript (at the end of a letter)
- 后记 (hòujì): postscript; epilogue
- 附录 (fùlù): appendix
These words are more usually used for describing postscripts though, not for introducing them.