Why would they put that "formerly Bergholt Sackville" bit? To help visitors using out-dated maps?
OK, so "Bergholt" means "hill wood"; it got its name because it was a wood on a hill (or, alternatively, a hill in a wood). Another village a few miles away also got this name. Eventually, to avoid confusion, they called the west one West Bergholt and the east one East Bergholt. East Bergholt is the one John Constable painted, and is therefore the more famous of the two. However, it's also in Suffolk, so the residents have to eat straw, sleep under sheep and fear witches.
But hold on, if the Bergholt in Essex was known as Bergholt Sackville, why would there be any confusion with plain old Bergholt in Suffolk? And even if there were such a confusion, wouldn't adding "East" to the Suffolk Bergholt have fixed it? Why change Bergholt Sackvile to West Bergholt?
Well, it was called Bergholt Sackville for about 400 years while the Sackville family were lords of the manor. When they stopped being lords of the manor, it stopped being called Bergholt Sackville. That was in the mid-1500s. In other words, it hasn't been called Bergholt Sackville for nigh on 450 years.
So why put "formerly Bergholt Sackville" on these new welcome signs?
I'm guessing that the council has the long-term aim to rename the village back to Bergholt Sackville, on the grounds that this sounds posher and will thus increase the value of all our houses...