Around 2003, Greenfield has erected new lampposts, mainly on Main and Federal Streets. One day, I noticed that, like utility poles, these also have ID numbers and letters. The difference is that they look handwritten and probably put there with a silver paint marker.
The ID's have two letters, followed by the number. I figured out what they stand for. The first letter stands for the first letter in the name of the street that they are located on. The second letter stands for which side of the street that they are on. The numbers are in chronological order, and start with 1, and keep going until the other end of the street. For example, one lamppost has the ID of MN33. This means that the lamppost is on the north side of Main Street, and is the 33rd on that side.
In the Energy Park area, the letters on the lampposts have the letters "EP," which obviously stand for "Energy Park." What is different about these is that there is no letter for which side of the street that these are on, probably because these are not on a street.
On nearby Miles Street, the lampposts have three letters on them: either MIE or MIW. That is probably because there is already another "M" named street with some of these lampposts on them: Main Street.
Lampposts from the Greenfield Gardens apartments also have ID numbers. They are just plain numbers, probably starting from the number 1 on.
There are also certain lampposts in Northampton that have ID numbers. Such lampposts that I know of are located near Damon Road.