If you are drawing walls and do not see the wall direction arrow you will need to check the color of the wall centerline in user preferences. If these colors are the same, you will not be able to see the direction arrow. ￼
Once the wall is drawn and if your background color is the same as your wall centerline color it will not appear on the screen.
You will have to make sure that your wall centerline color is different from the background color.
This is not something that by applying the color to the level will change, so you will have to redraw the walls in order to see the wall direction arrow.