http://www.my-english-club.com/email-writing.html

Agreeing with Michael..Did find.....2) The subject field, where you'll give a succinct indication of what your message is about. It is good practice to make the receiver of your email see straight away if (s)he needs to take action or just receive the information from you. You could use one of these words for this purpose: Re: = "regarding/referring to" or "in reference to"; FYI = "For Your Information" (no action required); Action = action is required and it would be good to also indicate the date the action is due; Urgent = this requires "Immediate Attention"; REQ = this is a "Request" for something