If the writing is on the wall for a person or an organization, it is clear that they will fail or be unable to continue.
However this photo shows our hotel room in Strasbourg where the writing was literally on the wall, which is a bit off the wall. Some people would call it grafitti. I guess it all depends on your perspective and how much you pay for a room.
BTW – “Off the wall” means strange or very different. Isn’t English fun!