I don't think that a Track Camera workflow is the best approach to your design. If you are getting a good Camera Track and the moving people don't foul up the track, here's one workflow that should work.
Step 1:
Camera Track the footage. Set an origin and ground plane, then use the same points to add a Solid and Camera to the scene. Run a preview to make sure the track is solid. Next, add more solids to other fixed geometry in the scene. I use solids instead of nulls because you can see if they properly stick to the surfaces. The trackers that follow moving people are not accurate and should be removed. If the people are not moving, you can attach a solid or a null to each person. When that is done, and you can verify that all of the surfaces you wish to attach a text layer to are responding correctly to the tracking, move on to step two.
Step 2:
Create the text layer with the text centered on the Anchor Point of the layer. Create a new shape layer that is big enough to fit behind your text layer and move it below the text layer. Make both layers 3D. They might disappear for a moment.
Step 3:
Select the reference Track Null or the Track Solid you created when using the Camera Tracker. Make sure the Parent/Link column is visible in the timeline (F4 should show/hide the column). Now hold down the Shift key and parent both the text layer and the background solid to the Track Solid or Track Null you created. This will snap them to the same position. Adjust the rotation of the text layer and shape layer to line them up with the shot. Move the background solid 1 pixel farther away from the camera in Z using the position property.
There you go. All Done.
The Camera Tracker will not accurately track people in a handheld shot unless they do not move. The Track Camera tool only accurately tracks fixed geometry. If you need to track people that are moving, the best tool is Mocha AE. If you use those options, you will end up with a track that follows the position of a feature region or the position, rotation, and scale.
The second best tool is the After Effects Track Motion Tool. The same Shift + Parent trick will work if you apply the tracking information to a Null, and this will allow you to track somebody moving all over the frame accurately.
If these tips don't help, we need to see your timeline and, if possible, the shot you are using.
Here's a zillion-year-old tutorial with no audio that I made showing how to track a face and add a graphic to it using Motion Stabilize. It is just one of the seven or eight workflows I use all the time to add elements (graphics, visual effects, etc.) to layers.
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