It stands for "Sorry For My English". Sometimes, as a non-native-english-speaker, you just want people to know that you are open to acknowledge a spelling or grammar mistake, or even to understand that maybe what you wrote makes no sense, without taking the full "Sorry For My English" phrase space.
*A really long email* SFME.
*Something that may or not be written correctly* SFME
SFME Do you car had of yello color??
Ruler of Lake Titicaca. Rumored to have a bunghole that gets very angry if it does not receive toilet paper. Cornholio the Great is often seen walking around with his shirt over his head and his hands in the air, chanting songs about his power, and his bunghole.
"I am Cornholio! You do not want to face the wrath of my bunghole, for I need TP!"
Butthead: Shut up, Beavis! (uh huh huh huh)
Beavis: Um, okay. (heh heh heh heh).