Aerosol Crimes

[Imp]

Are you having a laugh. If they are spraying for reasons stated there would be a dispersal patern. You would not have them criss crosing each other but rather most likely running parralel at set intervals. You would always do it at the optimum height to. So if appear at diffrent heights or criss cross its atmospherics.
Comercial airliners leave them to on occasion.
Military planes could indeed possibly use a form of spray to reduce friction but this would be sprayed over the wing surface as fine particulates to stop the air "sticking" to the wing. The results would be marginal but at Mach speeds might prove beneficial. However if the flow rate is slightly off it would probably cause more drag instead of less & could reduce lift.
A far simpler explanation is modern jet engines put out less emisions, these also produce finer particles which with the right atmospheric conditions hang in the air & produce what you see.