There is no standardized rule for this but many governments require or recommend that address numbers be displayed horizontally. This may be because numbers put together horizontally are easier to read as compared to a vertical display. It should also be noted that the alignment of the numbers should match that of the sign. Horizontal numbers on vertical signs or vice versa should be avoided. Your local jurisdiction may or may not have a specific rule about this, and we recommend that you check with them. You may also refer to our guide that covers some basic aspects of displaying address numbers.