Yep, scale.
You can use an oil spray- I use Neem Oil.
I have read about rubbing alcohol being wiped on their back as a good solution- dries them out or something..
Of course, you should remove all you can see by hand as well. Be aware they are probably actively laying eggs and more will show up, so it is important to spray every few weeks...
Good luck! I eradicated some off of a Trident Maple forest I have earlier this month. After a couple treatments and a bunch of rounds of picking them off by hand, I think they are all gone now.