Transit Tip 12: Keep pedestrian and bike paths free of obstructions.

There's usually a buffer space between the sidewalk and the street where signs, utility poles, mail boxes and other things can go. Bus stop signs, for example, must be placed 1-2 feet back from the curb so the bus mirrors don't hit them.  But if you get rid of the buffer area to add parking or maximize the driving lane width, don't encroach on the already narrow path for parking meters, construction signs or anything else that doesn't belong there. IMAG4720

Also, to all the highway engineers out there, if you put any objects on the sidewalk, remember that the sidewalk has been narrowed. It's not a 5-foot (1.5m) sidewalk if 2 feet are taken up by poles and signs.

This is a 2-foot (0.6m) clear width, less than the minimum required, even while the driving width is at least 30 feet (9m).

Check out Perils for Pedestrians has a wealth great info on walking paths.