Bonus Macro

Additionally, Riltia made this little macro to make it much more convenient to politely ask OOCers to stop doing so in public. What makes this even better is that a GM took a look at the macro, and said it was acceptable (he actually said a harsher version was acceptable, this is toned down).

/run local t="target" if (UnitName(t)~=nil) then SendChatMessage("Please talk in character, as Out Of Character (OOC) behaviour is against RP and server policy. Thank you for co-operating.","WHISPER",nil,UnitName(t)) end

Make it a button, then you can do this :
/target
Click the macro.
/ignore if needed.

If you want to change the message, just replace the part after SendChatMessage, in the quote marks, and leave the rest intact.