Signboard
Billboard, Store Sign
noun
A watch over board is a board that's put up and watches over everything. What kind of board watches over everything from up high? One that gets the most visibility, so probably a signboard or billboard.
看板 typically refers to physical signs, such as store signs or billboards. But it can also mean the figurative symbol or face of a business, like 看板メニュー (signature dish) or 看板娘 (popular female employee).
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
このレストランの看板は大きくてよく目立ちます。
The signboard of this restaurant is big and very eye-catching.
台風で看板が飛ばされてしまいました。
The billboard was blown away by the typhoon.
彼女はこの店の看板です。
She is the face of this store.
酔っぱらいの男が殴ったせいで、お店の看板がへこんでいるんです。
There is a dent in the store sign because some drunk guy punched it.