Store Sign
noun
A watch over board is a board that goes over your store and watches over everything. What board on a store watches everything? It's the one that gets the most visibility, so it's probably the store sign.
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.
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.