Grey primer? I've fitted new discs which were painted in this way to protect them. It wears off quickly when you use the brakes so no issues with braking performance.
Have done this with a company I worked for that baby sat 120 cars per month that were investments
Take the wheel off and spray it on, leave in gear or chock the wheels and hand brake off if it’s in direct sunlight you need to protect the tyres as they crack
If you can a cheap set of axle stands
I also write a paper note on the steering wheel saying no brakes, a mates unit was burgled and they left one car because of this all the others got pinched(3 out of 5) 2 had no brake paperwork