Treble gilt was used in the early to late 19th century to distinguish the quality of gilding on the front of the button. You find similar marks such as double gilt and extra gilt. There's not any standards to them as such, merely a indication that they used more material and hence more gold in fire gilding them.
The type you've got is a single face or open back style, which means its made much like a medal, rather than closed back, where they insert another piece to carry the button shank. That style runs from the very late 18th right through even to today, but was a popular manufacturing method on liverybuttons of the victorian and edwardian period.
The crown's possible a style of makers mark, but without a specific makers label it's difficult to date them with any accuracy.
Possibly Hammond, Turner and Sons who made sporting (hunt and livery) buttons in the 1840's and 50's are are known to have used a crown on some of their backmarks.