Samsung Calendar update adds stickers to the Galaxy S8/S8+ and Note 80
Galaxy S8, S8+ and Note 8.
For older models that have the S Planner app installed, a similar option allowed users to set various stickers for certain days. The new feature added to the Samsung Calendar can only be applied to schedule items save to My Calendar, so keep that in mind for when you try it out.
The new version of Samsung Calendar was released in the Galaxy Apps store last week, so it should slowly appear for everyone in the coming days.
source: XDA Developers