Signs and command blocks can be placed with commands without op

With the blockEntityTag feature introduced in 1.8 the tile entity of a block can be stored in a item and placed exactly as it was created. This also works for signs and command blocks allowing for survival players or non-op'd creative players to place command blocks with pre-created commands down (same for signs)

To make this worse signs still run commands at a higher level than command blocks allowing a player to be op'd by a sign.

And even worse: A player in creative with client mods can create a sign/command block with a tag and therefore not requiring an op to even create the first version of the block. This allows any creative player to get op quickly.