Quote Originally Posted by Eye_Gore View Post
You speak with the guild receptionist, near the door when you enter, but if there is no quest icon above them, then you have not reached a high enough level yet.
Pretty sure the bolded part is incorrect, but the rest is true. I don't think there's anything advertising those quests. The receptionist will give you some expository text, then they'll give you a yes/no option if you're still interested in the guild, and if you say yes, THEN the quest icon will show up.

I'm pretty the requirement to join other guilds is that you have completed the lv10 class quest for your current class before you can join any other guild.