You’ve also seen it in Settings next to the Control Center line, as mentioned above.the only place so far that i have seen that icon in iOS12 is in iOS' new Shortcuts app, which also allows the app to place on the the Home Screen an icon as well.
does the line under the icon in yr photo indicate it wants you to swipe down?
Try swiping down with your finger starting just above the screen ie above the battery icon tokI havent installed that app, and i cant swipe that icon in any direction
You’ve also seen it in Settings next to the Control Center line, as mentioned above.
My guess is it shows this if you’ve never used it as a tutorial but then disappears once you’ve used it (a few times?). Then it defaults back to just the more cryptic line.