There was a promotional mini-game called Sigils of Elohim, released by Croteam prior to releasing The Talos Principle.

https://store.steampowered.com/app/321480/Sigils_of_Elohim/

The desciption says:
"Acquire items and relics in Sigils of Elohim on PC, Mac, and Linux that transfer over to The Talos Principle on PlayStation 4, PC, Mac, Linux and Android."

Does anyone know what items are unlocked? Are they available in the GOG Gold version?

If anyone is sitll wondering, you can unlock up to 12 rewards by completings Sigils of Elohim (slight spoilers ahead) and entering the codes:

1) 3 Bonus Stars

2) 3 Bonus Messenger Hints

3) 3 additional options for your player message QR Code:
- "These sigil locks come naturally to me. Perhaps I have some Russian in my lineage."
- "I took time to prepare myself for the obstacles in this world. It was time well spent".
- "I don't care what people say, I'm just here for the sigil locks."

4) 3 extra options for your epitaph:
- "I did my bit. Just don't ask me to help with any more sigil locks."
- "Why is the wall so crowded? I thought I was special."
- "I don't know about the puzzles, but I'm a professional sigil-arranger if you need help there."

I am also looking for the answer to this question.

The unlocks are not available the Steam version, because they apparently required phoning home to their server, but they have shut the server down, so it just gives an error when attempting to redeem.

It's possible that they removed this "phone home" functionality, and it works offline in the GOG version.

Does anyone know?

I can now confirm that the GOG version does NOT have the "Redeem Rewards" option in the main menu, and there is no way to enter unlock codes from Sigils of Elohim.

While the GOG version includes the DLC, it does NOT include the 2 demos that are included in the Steam version.

It also does not include any achievements, so although the game has a built-in achievements list, the devs chose to completely strip it from the game instead of allowing people to unlock achievements offline. Pretty shameful.