in the subject line of an e-mail, (nm) stands for no message. that is, the sender is so to the point that he needed only the subject line to express himself, so there's no need for the reader to open the (blank) message.
Subejct: Your house is on fire. Run for cover. (nm)
Prices shown in USD.
Type your email address below to get our free Urban Word of the Day every morning!
Emails are sent from email@example.com. We'll never spam you.