Look at the history on these. Any thoughts as to what they are up to?
N857GA is categorized as aerial advertising and patrol by the FAA:
registry.faa.gov/aircraftinquiry … rtxt=857GA
N62923 belongs to a company involved in aerial photography and remote sensing: richardcrouse.com/
Ya just adding to Dave, you can check N-Numbers at the Resources section on the bar to the left. flightaware.com/resources/registration/N99999
Flight check aircraft.
No. A flight check aircraft checks the navigation systems such as ILS and VOR. These aircraft doe remote sensing (e.g. geological studies) and aerial photography.
I checked the resources page you mentioned. The FAA page, though, is more detailed.