Where should I put 911 emergency or grid address numbers on a street sign?
The typical location for the adress grid/911 numbers is directly below the St, Rd, Ave, etc. at the end of the sign. The minimum size of these letters and numbers is one-half the main letter height or 3 inches, whichever is larger. This will require some adjusting to provide proper alignment of the text on the sign.
6-inch sign letters will require 3-inch St, Rd, etc., and 3-inch address numbers. For the smaller 4-in font sized signs the St, Rd and 911/grid numbers would need be 3-inches in height still. This would require a longer blade with the numbers to the right of the type of road (St, Rd, Ave, etc.).
Be sure there is at least 1-inch of space between any row of letters, row of numbers and the border (or 2-inches for street signs without a border).
Street Name Signs in the MUTCD (see section 2D.43)