There is no clear explanation of its name, but various sources tell of the island being used as a place of refuge by some Irish and English princesses.

In 1545, Gustav Vasa made an appeal to the citizens of Eckerö to make it a protected port and a shelter to sailors.

Signilskär received an important function in 1638 when a mail route was implemented between Sweden and Finland, which then belonged to the Swedish Empire.

Crews navigating the dangerous passage between Sweden and Åland in frail postal boats could end up facing heavy weather, in which case they could find shelter on Signilskär and wait for conditions to improve.

The most important function it served was being able to quickly receive war threats from the east (namely Russia).

[1] The islands border on two busy shipping routes in which oil spills and major disturbances of animals tend to occur, a potential threat to the wildlife, especially in the breeding season.