When your sleep, readiness or activity score is excellent (above 85) , you'll be awarded with a crown.
The crown for readiness is shown above your readiness score in the main view. Crowns for sleep and activity are shown on the left side of the timeline items. Crowns are also visible in the detail views.
To get an overview of past scores, tap the calendar icon in the bottom left corner of the main view. A crown is shown for each day you've received at least one. You'll also see a small dot representing each score under the day number (starting from the left with activity, sleep and readiness).