You could try adding a comment line to the .pz3 file. Fairly easy using the standard Python file handling routines.
Before rendering, your script could read in the .pz3 file and scan for the comment markers ( // ). The name of the .pz3 file is known when you're batch rendering.

It's probably wisest not to add those comments on the first line of the .pz3 file. I'd try inserting those comments right after the version info. That way, you'll only have to read a few lines from the entire .pz3, saves a lot of memory and will speed up things. Also, the first occurence of something that is NOT a comment and NOT version info indicates that this .pz3 doesn't have markers, so you can stop scanning and close the file.

Another option would be adding an invisible prop to the scene (a box or a plane, something simple). Set its internal name to PropertyObject, and its name to a string that's useful to you. At render time you can access poser.Scene().ActorByInternalName("PropertyObject").Name(), and you'll have your property string.

The pen is mightier than the sword. But if you literally want to have some impact, use a typewriter

My gallery   My freestuff