Decorations can be used by farmers who put their town hall in the corner to indicate that there are no traps surrounding the town hall.
Farmers want people who can't attack their bases to destroy their town hall, because it protects their loot with a cheap shield. Some people put their town hall in the corner, but surround it with traps. Decorations surrounding the townhall lets the attacker know that the farmer is giving away their townhall in good faith.