Right-clicking on a freestanding sign

If the sign is already facing you (such as if you've already turned it once), then it turns 180 degrees around. If a sign is mounted on a block, right-clicking it will flip it around.

Sometimes if you have placed a sign on a flat surface the orientation just doesn't look right the first time. So you either have to live with it or you break the sign and retype whatever text you put on it. But it would be more convenient if you could pivot the sign in place and adjust it without starting over.

The first right-click makes its face perpendicular to yours, and a second right-click (assuming you haven't moved) flips it 180 degrees around.

None of these actions should break the sign or erase the text--but these actions would be handy for hiding or revealing information one sign at a time. Letting turn it 180 degrees around or turning to face the player when they right-click it would let it act like a revealed message or easter egg to another player. 

Flipping or pivoting a sign could also send a redstone signal, enabling the sign to be a kind of single-use button that contains a short text message (which could be good news or bad news depending what the sign's signal just sent power to). If this would seem too overpowered, then you could make a special variant sign that requires a stick, one redstone dust, and five wooden planks of any type to make a wood-agnostic sign that can interact with redstone wire in this way.