Ättestupa may literally mean something like "old man's fall". The sign explains this.
Ättestupa is a tradition or legend that says that old people in Nordic antiquity would jump or be thrown to their deaths by making a steep leap.
According to the myth, this happened when older people were no longer able to earn a living or contribute to the work on the farm. Many places in Sweden and the Nordic countries are said to have served as family graves, but it is no longer considered likely that they were actually used.
The series "Norsemen" starts with an Ättestupa. Directly from Season 1 Episode 1 in the second minute.