Ok, these are good points. I can definitely see this being needed. I've got an alert added for next update, so while you are online if anyone is chatting in the guild group chat, a little bubble will appear with the number of unseen messages in it. It will not play a sound (as that might be annoying).
Currently it will NOT display unseen messages when you first login, only unseen messages sent
while you are online. I figured this is probably satisfactory. Although if players really think a bubble with new messages when you first login is really wanted, I can add that in the future.
Here is a picture of how it will look.

- guild chat alert.png (227.1KiB)Viewed 383 times