Hey guys and gals!
I don't believe you can change your avatar from your mobile phone. If I am wrong let me know and I will edit my post.
To update your Avatar:
-Click "Welcome, ________ ". (upper right hand corner)
-A tab will come up.
-Select "Edit Profile".
-A new page will load. Above the 'Preferences' bar and below the ad banner are a few selections, one of them being AVATAR.
-Select Avatar, and change you image by using the 'Browse' button.
Signatures:Putting info in your signature gives other members opportunity to see your personality. It can also be a way to show off some of your achievements as a player in ARR.
I used xivreborn.com to make my own signature. You just put your name and server in, no passwords or anything.
Hope this helped!
-Poo