The sign band width has to do with the store front or building. Most cities do not allow for anything over 75% of the usable area of the front or back of the building above the doors. This is measured from the inside of the building walls. and the height above the doors. Example: If you have a wall 20 long and the usable above the door is 5 foot that is 100 square feet of which you are allowed 75 square footage where the sign can be installed. This determines the biggest size sign allowed.