LocationIDs are used to name areas within a zone. These names will show up on the scoreboard as your location when you're inside that area. By default UT has a spherical shaped locationid, this can be found under Actor->Keypoint->locationid. Simply put one down at the point you want to mark and set the radius accordingly. Note, it can be useful to right click on the bar at the top of your view and choose "Views->Radii view", then bring up the locationid's properties, set bCollideActors to true and then adjust the CollisionRadius. You will see a circle marking the radius which you can use to position the locationid. Be sure to lower the CollisionRadius and turn off bCollideActors when you have placed it.
Thievery has two more location id's which are of use: