Writable Items can have text on them that appear when looked at or used. Some of them are Rewritatble, i.e. the text on them can be edited or erased.
Please note that some of the non-rewritable items aren't found in game in their blank state. Some are part of the map and are written by default, while others can only be created by CipSoft members and are usually delivered with text on them, such as Contest Prizes.