Cloud seeding is an old idea that specifically refers to attempting to produce rain from otherwise "normal" clouds. They use a cannon or plane to put (usually) silver or potassium iodide in the clouds, which gives the moisture something to condense around (nucleation) and hopefully fall out as rain. Now, calling something a cloud seeding (or anti-global warming, for that matter) operation could be used potentially as cover for something more sinister, but by itself cloud seeding is fairly benign. From what I know of it, anyway. The Wikipedia page may prove informative: https://en.wikipedia.org/wiki/Cloud_seeding