If you are in Adventure Mode with a sword, then you can attempt to break signs. The signs won't break though, but they act like they are being broken.
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marcono1234
MC-96667
Signs can be broken with swords in Adventure mode
Resolved
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0
marcono1234
goalreadymc
(Unassigned)
Unconfirmed
Minecraft 16w05b
Retrieved
Probably duplicates either MC-8472 or MC-19676