@BreakingPoints and for the community since nobody has talked about it directly,

Helldivers 2, which the CK shooter seems to reference with the inscribed arrows, is a deeply satirical shooter game that is a spiritual successor to Starship Troopers.

The game has players engage in an interplanetary war to defend "Super Earth" from alien bugs and robots, in which the governing body of Super Earth is clearly fascist and players are expendable helldivers who are sent to foreign planets on missions to do various things, but mostly clean up the mess of the governments experiments and other alien incursions.

However, the fun of the story aspect is that it is very tongue-in-cheek patriotic such that you are routinely told not to question things less you be deemed a traitor. You have to destroy radio towers that broadcast conspiratorial (factual) news, and you always get the sense that there's a deep well of fascist darkness just behind any question you may ask.

Since you are deployed on foreign planets, you logistically need to get there. That function is performed by starships, which players create upon firing up the game for the first time. You are encouraged to name your ship something patriotic. The options are literally limited to patriotic words, which players sometimes turn into deep dark satire. Others don't get it and believe it to be based.

From your ship, your helldivers are deployed to the planet it hovers. As a helldiver on the planet fighting against giant bugs and robots, you need more support or artillery than you can carry, or you need resupplies. These supplies are called in by spherical beacons you throw on the ground which the spaceship tracks and launches in a pod directly onto the beacon.

You can call in all sorts of things, rifles, exosuits, mines, lasers, rockets, and, 500kg bombs. The way the player selects which beacon to throw is as simple as pressing the corresponding direction on their gamepad/controller in the correct order. For the 500kg bomb, the order is up, right, down, down, down. Then you throw the beacon, and a few seconds later, the bomb lands nearly on top of wherever that beacon landed. The 500kg bomb stratagem code is the arrow inscription the CK killer used.

So I think what people have missed, including our hosts, due to chalking up the HD2 thing to "video game lulz", is that HD2 is a very particular type of game. It isnt just fun, it has some biting social commentary in it, and like so many other things in our society, you can find a group to play the game with that understands and has fun with the satire, and you can find groups that view it not a satire but as a utopic ideal in an unideal setting whic is entirely based.

I don't know which of these groups the CK shooter fell in, but it seems like he is smart enough to get satire, which makes the HD2 choice extremely interesting. Not just to use it as a reference at all, but he didn't inscribe the stratagem code for the various "sniper" rifles in the game, though he allegedly used one. I don't know what to make of it all, but I do believe it's quite uninformed to discard the using of HD2 as a message. There are hundreds of thousands of games he could've found cause to use as a message, but this is the one he chose.

EDIT: One topic i wish i had included in the original quick write-up is the subject of death. In this game, the helldivers are expendable. When one dies, another is fired down from the starship. Each mission has a budget of how many helldivers can be expended. It does increase slowly over the course of a mission if you lose too many too quickly.

Players are meant to know that each helldiver is different, as if you don't change the default setting, the next diver deployed after the one you were playing dies will have a different voice, body type, and perhaps gender as well.

Additionally, being deemed a traitor or defector is a death sentence. You will be shot via orbital cannon if you go outside the borders of the mission for too long.