I have seen it on Mac, but can't find it on Windows.
There can be two reasons for the icon not showing up.
Sharing in Photoshop 19.0 require the Windows 10 Spring Creator's edition. Maybe you have the "Anniversary" edition?
A second issue could be that Sharing becomes deactivated if you install Photoshop to a location that contains non-Roman characters in the file path.
Quick share icon does not appear on my screen. I am sure I have the new PS CC (tools on the right have demo tool tips, I have the learn feature on my window menu [not sure why i chose me] and I have switched to the default workspace.). I opened a file from LR, I opened a file synced from LR mobile and I tried a new file.