witchdoctor says....
"If you consider that any carbon based fuel produces water and carbon dioxide as a by product of combustion, then even your car would produce contrails if you got it high enough. So piston or turboprop, it doesn't matter."
Aviate 1138 says from a cold Britain.....
On a cold morning when you start your car [presuming it is not a smoky oil burner] what do you see coming out of your exhaust? Yes! A low level contrail! As for the piston engine question there are plenty of photos of high flying piston engined aircraft making rude signs [ penis and testicles] over London during WW2.
I gather one or two USAAF Mustangs did the same thing over Berlin.
Aviate 1138