Runestone

Runestones are signs, which you can place as various notes. Each runestone can hold 100 characters. They can be lifted and moved. Once inscribed, the message on the runestone cannot be removed or altered.

How to Acquire
Use the Carve Runestone action on a boulder or rock.
 * uild > tone Working > unestone

How to Use
After the runestone is carved, you can click on it with the right mouse button to carve a message. That message cannot be altered later.

When you write more than 100 characters on the runestone, the game will tell you that you have too many characters.

How to Remove
Carry the runestone and walk into shallow water. Next, log out while you are still carrying the runestone above your head. When you log back in, the runestone will have disappeared.

You cannot simply place the runestone into shallow water (the game will tell you that you cannot place things in water).

Source: Forum post made on Feb. 15, 2011.
 * You can also simply destroy runestones like other liftable objects. It may take awhile.