If you rename a sign using an anvil and place the sign anywhere, when you break the sign, it is named "Sign" rather than whatever you previously named it to.
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migrated
MC-49119
Named signs losing names when placed
Resolved
Duplicate
0
migrated
migrated
(Unassigned)
Unconfirmed
Minecraft 14w07a
Retrieved
This is the same for any "Block" that can be placed after naming in an anvil.