The best I can piece together, as a layperson reading state statutes, is because the NH Division of Historical Records[1] was assigned a duty and a budget to preserve and disseminate information on NH history [2]. The NH Historical Marker program is a joint effort with the NH Department of Transportation, and it is the responsibility of the DOT to erect and maintain the signs after approval from the Division of Historical Records [3]. The DOT has authority to erect these signs on class I-III roads which are state owned and maintained [4].

There appears to be a separate statute governing the installation of markers along class IV and V roads which are maintained by cities and towns [5].

[1]https://www.nh.gov/nhdhr/about.html

[2]http://www.gencourt.state.nh.us/rsa/html/XIX/227-C/227-C-4.h...

[3]https://law.justia.com/codes/new-hampshire/2015/title-xx/cha...

[4]http://www.gencourt.state.nh.us/rsa/html/XX/236/236-40.htm

[5]http://www.gencourt.state.nh.us/rsa/html/XX/236/236-44.htm

We do the same in Germany. It's so you get interesting buildings and other things pointed out when driving through an area you don't know well.

There are many interesting places between A and B. You know about A, because you're living there. You know about B, because it's your destination. Typically, you've never thought much about the in-between.

There are all sorts of historical markers on various things and in various places all over the US. (Though I'm not aware of any at Dartmouth College regarding the computer-related events that occurred there.) These particular markers are ones put up on NH state highways where they're fairly visible even to people not actively looking for them.

If I recall, there is a plaque in the lobby of Kemeny Hall at Dartmouth about Kemeny's role in creating Basic.

New Hampshire has these green historic signs all over the place - they are particularly thick in the seacoast region, for historic buildings or places where events of any kind of significance took place. For example, in downtown Exeter, there is one by the town hall commemorating a speech that Abraham Lincoln gave during his presidential campaign, also noting that his son went to Phillips Exeter, and across the street there is another marking that Exeter was once the capital of New Hampshire, and then a couple hundred yards away there is another marking where a tavern still stands that George Washington once ate dinner.

Later in life, Lincoln's son, Robert Todd Lincoln, built a large house called Hildene in southern Vermont that was occupied by descendants into the 1970's. It is maintained as a museum. It's pretty interesting and worth a trip, if you're into that sort of thing. Even my two teenagers found it interesting ;)

https://en.wikipedia.org/wiki/Hildene

There's also a plaque in Dartmouth Hall about the Dartmouth Summer Research Project on Artificial Intelligence, considered the founding event of AI research.

Most of these, in most states, are either beside roads or on buildings. I suppose it allows marking things that aren't buildings (or associated with one building). It also allows making far more visible, due to our car culture.