Contrails?

U.S. Patent 3844199 (1974)

Abstract;
Light scattering pigment powder particles, surface treated to minimize inparticle cohesive forces, are dispensed from a jet mill deagglomerator as separate single particles to produce a powder contrail having maximum visibility or radiation scattering ability for a given weight material.

Source: Official US Patent Archives @
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=3899144.PN.&OS=PN%2F3899144&RS=PN%2F3899144