On the west coast I've seen 3 distinct different trails. The contrails are most prevalent these often disperse rather quickly, the other two types are often done before storms, one is used to keep it from raining and often spreads out to cover most of the sky in a haze. The last is used to promote rain and you'll see them coalesce and start forming clouds.

Granted the people in the know will still have you believe weather modification or cloud seeding is still being done with bi-planes with bottle rockets fixed to the wings lol, but they moved onto drones and jets a long time ago.