Car owners everywhere curse wild birds. Why? Because birds never invented the toilet, having a habit of living in trees and allowing gravity to take their poop away. Where it hits things down below, like cars.
The biggest threat to cars is the ammonia, which damages the paint. This can be prevented in the first place with waxing and/or covering the car while it's parked. But let's say you didn't do that and there's a splat. Now what?
A rub with soapy water will remove it, and many guides swear by peroxide. Perhaps a car with a pH detector that squirts a vinegar-peroxide mix at any region with rising pH (though pores in the paint)? Nah, that's crazy.
Just clean it more than this guy, who I think left his car there for months. (Perhaps out of state on business?)