Driving around New York City on I-287 in Westchester County, the signs used to say
No White Plains
for North White Plains. See, for example, this picture from this webpage. They've recently replaced these signs with ones that say "North White Plains", probably because they confused tourists.
You also see signs "No Brunswick" and "So Brunswick" for North Brunswick and South Brunswick in New Jersey, southeast of NYC.
My understanding was that N. and S. were the standard abbreviations for "North" and "South". Where are "No." and "So." used? Is it just New York City and its suburbs, or is the usage more widespread than that?