They may have a Snapchat+ badge next to their display name
Their profile may show a Snapchat+ subscription section
They may have custom app icons or themes enabled
They may have a custom chat wallpaper or profile background
They may have a Story timer or Story expiration features not available to standard users
They may have access to exclusive Snapchat+ features like priority story replies or best friend solar system
Their profile may show a star or other Snapchat+ indicator depending on app version
They may mention Snapchat+ features in their profile or posts