Many Piston Aircraft left contrails in the war, this was at very high altitudes however. And yes the recon aircraft had to be very careful of this, in fact so did some bomber missions, small numbers of aircraft doing precise bombing runs to very sensitive targets. They sometimes used chase aircraft and scrubbed the mission if contrails were forming.
I have seen wingtip vortices off light aircraft in very humid conditions though and I, as other have suggested too, suspect that it is these that are the subject of the topic.