Following up on this post from a couple weeks ago, I’ve found another place that takes “ha ha” as its name. Strangely enough, I saw both of these signs on the same road trip. This one was somewhere on route 915, near New Horton, NB.
I take it naming a cemetery “Ha Ha” wasn’t seen as odd in 1800. According to this page and this historical map, the nearby bay was once called “Haw Haw Bay.” This page, meanwhile (copied from a plaque on the site I think) says that the name comes from a first nations word for the call of a loon. Apparently New Horton Lake was also once called “Ha Ha Lake,” but at some point they realized the name needed to change.