Since 2016, there is no more physical Slovak motorway vignette and now is fully electronic (e-vignette), meaning stickers are no longer being used.
The e-vignette is linked to the vehicle license plate and is scanned and checked in the digital toll road system.
You can order your Slovak e-vignette comfortably here.
Related articles:
What different types are available for the Slovak e-vignette?
Where can I buy the Slovak motorway e-vignette?
How is the Slovak e-vignette checked?