I found a couple mods that appear to do what you need.
This is the mod that will show who is currently assigned, if any, and allow you to assign directly from the ticket list.
http://www.osticket.com/forums/showthread.php?t=2719&highlight=assign(http://www.osticket.com/forums/showthread.php?t=2719&highlight=assign)
This mod is a much simpler mod to do, and will just add a column to show who is assigned.
http://www.osticket.com/forums/showthread.php?t=1068&highlight=assign(http://www.osticket.com/forums/showthread.php?t=1068&highlight=assign)