When you finish a subject line with an ellipsis ..., it's customary to have the subject line continue in the body of your message.

If your subject line is your entire message, it is a courtesy to indicate so by means of "eom" or some similar indicator. This is a courtesy to your fellow Board members so they do not waste time opening messages with no content.

Have you noticed how many reads most threads with an "EOM" get anyway?  It's a courtesy that doesn't seem to matter.