If you detach S Pen and unlock tablet with that, you may see a ink effect on the screen. Disable or enable ink effect on Galaxy Note 8 or change ink color by doing as follows:
1. Open "Settings" App
2. Go to "Lock Screen" and tap "Lock Screen Options"
3. Tap "Ink Effect"
4. Choose "None" to disable ink effect on Galaxy Note 8
Choose from colors, to enable ink effect on Galaxy Note 8 and change ink colors