Those are called 'scale bugs', and there are many types of them. While they are damaging in a big infestation, as far as grow pests go they are not the worst bug to have!

Gently scrape the adults off with the tip of a knife, being careful not to damage the stem, and treat the grow area with a pyrethrin bomb to kill vulnerable life stages. If you are more than 3 weeks into flower, you may be stuck picking the adults off manually. Luckily they do not breed as fast as other growroom pests and manual removal is actually an option.

Periodic light sprays with neem oil- LIGHT being key here- will make your plants' surfaces so distasteful to insects as to prevent them feeding. This is organic and safe to use at any time, but the smell is not so good and you should stop applying it after week 3 of flower.

Hope that helps, and welcome!