These look like scale insects, which suck the nutrients out of the leaves and branches and if untreated, can seriously damage a plant. If you scrape with your fingernail and it pops off, it’s scale. Underneath each hard, brown shield is a sucking insect. If there are only a few, wipe them off with a Qtip dipped in rubbing alcohol. Sprays cannot penetrate the shell, but mature insects cannot reattach. The immature ones are hard to see, but they are vulnerable to spraying. Test a mix of one part mineral oil, one part soap, and eight parts water on a single leaf, to make sure it doesn’t damage the foliage. After 48 hours without signs of damage, go ahead…and if you see signs of burn, reduce the solution and retest.