Games like SIGNAL
Games like SIGNAL include Firewatch, What Remains of Edith Finch, Layers of Fear (2016), The Beginner's Guide, and Amnesia: A Machine For Pigs. We matched them by the tags players give SIGNAL on Steam (Adventure, Walking Simulator, First-Person, Horror, and Atmospheric): closest matches first, and among equally close ones the better-known games.

Firewatch
Shared: Adventure · Walking Simulator · Atmospheric

What Remains of Edith Finch
Shared: Walking Simulator · Atmospheric · Story Rich

Layers of Fear (2016)
Shared: Horror · Walking Simulator · First-Person

The Beginner's Guide
Shared: Walking Simulator · Story Rich · First-Person

Amnesia: A Machine For Pigs
Shared: Walking Simulator · Horror · First-Person

Outlast
Shared: First-Person · Horror · Atmospheric

Little Nightmares
Shared: Adventure · Horror · Atmospheric

Blair Witch
Shared: Adventure · Horror · First-Person

MiSide
Shared: Horror · First-Person · Story Rich

Among the Sleep - Enhanced Edition
Shared: Adventure · Horror · First-Person

The Beast Inside
Shared: Adventure · Horror · First-Person

Still Wakes the Deep
Shared: Horror · First-Person · Walking Simulator

SOMA
Shared: Horror · Atmospheric · Story Rich

Mouthwashing
Shared: Horror · Atmospheric · Story Rich

Little Nightmares II
Shared: Adventure · Horror · Atmospheric

Hellblade: Senua's Sacrifice
Shared: Atmospheric · Adventure · Story Rich

Gone Home
Shared: Walking Simulator · First-Person · Atmospheric

Bendy and the Dark Revival
Shared: Horror · First-Person · Adventure

METRO 2033 Redux
Shared: Atmospheric · Horror · Story Rich

KARMA: The Dark World
Shared: Walking Simulator · First-Person · Horror

DEATH STRANDING DIRECTOR'S CUT
Shared: Walking Simulator · Story Rich · Atmospheric

Metro Exodus
Shared: Atmospheric · Story Rich · Singleplayer

Poppy Playtime
Shared: Horror · First-Person · Singleplayer

The Hat Man: Shadow Ward
Shared: Adventure · Horror · First-Person