I'm pretty sure that if the police are trying to track someone down to bring them in for questioning or whatever and they can't find them at their house that its standard procedure to make note of vehicles parked there, license plates and stuff, simply because it could offer more leads towards tracking the person. Or if they suspect someone of a crime they would note vehicles as well so that they can pull said vehicles over. (Potential getaway cars/known associates of suspects, etc.)

Also cops tend to note plate numbers and such for any and all or even no reason sometimes, nowadays many cop cars have cameras that document every plate they see and cops will run your plates just sitting behind someone at a stoplight.

But beyond all that, just think about it for a second, we see how thorough an investigator Hank is, why wouldn't he investigate/document an R.V in Jesse's driveway whilst trying to track him down?