The Icon Overlays are missing for my sync folders and files in Ubuntu 17.10, they were working for 16.04?
Note: I have made a completely new install of 17.10
Yet Icon Overlays are working fine for another cloud based file hosting service, viz. Dropbox
Solved!
It turns out that the original automated install of the insync-nautilus deb package failed, which allows for the overlay integration with Nautilus.
Solution: Go to the https://www.insynchq.com/downloads page
Open Download for Linux
Select Packages tab
Download the Nautilus deb package
Install the package
Then either restart Nautilus or Log out and back in, to see the overlays