The Billboard is one of the five Progressive Era decorations and can be build after researching Tenement Houses. When the Billboard is polished, its output of happiness is doubled for 12 hours. Decoration does not need a road connection. The sign also has the word Led Zeppelin which could be referencing to the famous 1970's rock band.
+61.5 per tile.
Your decoration can be polished to double the happiness provided to +36 for 12 hours.