The signal

Established in Season One

• The broadcast has unusually regular timing.
• It repeats an unfamiliar phrase.
• It names a future date.
• It passes through multiple relay points.
• A map's coastal relay point is crossed out.
• At the finale it shifts offshore, and a light answers from a dark ship the group doesn't recognize.

Still unanswered

• Who or what sends the broadcast?
• What do the phrase and the date mean?
• Who marked the coastal point, and why?
• Did the ship send the signal, merely hear it, or is it unrelated?
• Who is aboard, and what do they want?
• Does the rumored refuge exist, and how does it relate to the relays or the ship?