By Valefor.Surivere 2013-05-17 05:35:29
There is no official way to tell.
Best case is just listening to rumours, hearsay and shouts. Most groups who do these things tend to advertise this well ahead of time, mentioning it several times a day. As well as have a shouter(mule) in town telling people they are currently fighting it.
When one is going on, it's hard to miss. The problem is more that these fights happen so rarely, it's kinda sad ._.;