You can customize the text and logo for each organization in the system.  This is the text and logo that appear when a user who is a member of that organization will see when they first login.   Only administrator can make changes to this information.

To do so, edit the organization by clicking on the Manage Domains link on the frontpage.  Find the organization you want to edit in the drop down and choose Edit Organization.  Now in the form, enter the Intro Page text - you can use relatively unrestricted HTML here.  Now choose a company logo.  There are no restrictions on this image really though it should be a JPEG, GIF or PNG and not much larger than 128x128 to fit nicely in the default theme.