To find Informal Salutation you will add the Object User Address to a User Base if it's not already there. Once added you will:
  1. Click the Display Fields Tab
  2. Click Select Fields
  3. Expand the Categories until you get to User Address
  4. Under User Address Check Label Salutation 
  5. Click Select
In lists the Label Salutation Field corresponds with the Informal Salutation entry for Users.