I think they use actual DNA, probably something dish-grown and standardized, with a sequence designed to stand-out.
The reason is that it's both entirely harmless, and can be revealed using existing DNA-testing infrastructure for reliable prosecution.
Even a small particle on a suspect's skin may be enough for identification.
I wonder if certain kinds individuals will start wearing synthetic, disposable clothing that is resistant to such tags.
This will likely be limited to certain units and situations - like riots.