Usually on the UAG logon screen the Authentication name will be prefixed in the password field.
For instance if you have integrated with Active Directory and you have put the NetBIOS name as the Authentication name for your Active Directory authentication, your NetBIOS name will be advertised on your logon page.
If you want to tighten security and remove the Authentication name, you will need to edit the Login.asp file and remove the following text:
or if you wanted to prefix your company name, just edit String 109 in the relevant languages file. See this post for more info.