Simple text on any object / I want to write on a wall in my game . How to..?

Hi there, I know this is a most discussed question, but none has really answered a fully justified answer yet (or I haven't found it yet). What I want is to make a wall / board that has text on it. The wall can be a quad, a plane, a cube, anything that stands in space, and on it and only on it, I will be able to adjust a textbox and write on it. I want to be able to order the text area, change the text dynamically (remain text - object) and the player will see it only when stand in front of it.

I have tried 3d-text, but it is not fully adjustable (I was never sure where the textbox lies, and it can be seen from any angle (nothing hides it) I also tried a tutorial to change its texture/shader (sth over the Unlit shader with a given scrpit), but did not work (got squares instead of letters). I also changed canvas to world space, made it child of the board-object but still it was somewhere in the air over / near my board-object but certainly not what I wanted.

So anyone knows a good way to "write on a given wall / board" , or knows a secret script or anything, please help...