Get an alcohol pad. Wipe them off. You have soft-shell scale as a few guys indicated. The insect lives permanently under the shell and is impervious to many insecticides.
The alcohol won't affect the plant at all. Since you have a pretty heavy infestation you'll need to do it weekly.
Your plants would make an excellent show and tell for many growers, both new and advanced because not only is it a good example of soft-shell scale but if you look carefully with a magnifying glass you'll see the whole life cycle of the insect from egg to crawler to adult all on one plant.
Scale exude a sticky, gummy substance called honeydew. The honeydew attracts ants if outdoors and a secondary infection called sooty mold. Its black and unattractive but doesnt harm the plant.
Don't use any insecticides as they aren't really effective and not necessary in your case.
