Maintain 100 (shown by a :D emoticon in place of a number) or higher Happiness for a 14 in-game days and you'll be rewarded with the beacon. Like The Statue of the Key, it is free to construct, but only one since it is a unique building. Can only be placed on the ground or a rooftop.
The Beacon has been designed together with Annabelle, who won the first building contest in the Discord.
At night, The Beacon will be brighter.
the Beacon shining at night - Pictured by ElvisFrost157