A good bit behind the curve as other games have had a second name or Surname available for a while, but better late than never.
On the PTS at the moment is a scroll that will allow you to add a 'last name' to your char. It's a credits only purchase, applies only per char and costs 2880 credits. All this of course, subject to change from the test server.
Lead Dev Pithos also posted what can and can't be used:
Source: http://forums.riftgame.com/general-d...ust-1-a-2.htmlLast names must be at least two characters long.
Last names cannot contain two spaces in a row.
Last names cannot start or end with a space.
Last names can be made up of multiple words.
Each word must be at least two characters long.
Each word can contain up to one apostrophe.
Each word can contain capital letters only as the first letter, or immediately after an apostrophe.
No numbers or other punctuation beyond spaces and apostrophes.