An ingame notification (in the envelope on the top-right) should appear when there are changes in the guild you are in. For example, you will be notified when you're position in the guild was changed or if you were kicked (correct me if there are already notifs about being kicked), and the most important, notifications in any changes withing the guild message.

I've suggested about the notification because I lead a guild and I often use the guild message to inform my members for party formations and events in the guild, ingame.