I've just re-watched that scene a couple of times & you're right - there's a red spot appears at various points.  I also thing there's a slight red cast on Mr C when Duncan Todd is speaking to him.
I've no idea what it means though!  🙂

Someone with a laser sight, perhaps?  Ray?

It's more diffuse than a laser - maybe 2 - 3 inches across...

I agree but... a laser will scatter if it's passing through glass, particularly dirty glass.  I wondered if someone was drawing a bead on them from an old outbuilding somewhere else on the farm.

I readily accept it could be something else, though.

 There are laser listening devices that can pick up speech when aimed at glass.......more likely that the director of photography showed it to DL just after the scene was shot and DL said "not worth re-shooting, we're done here".

I completely missed this the first time and definitely I think it was intentional.  Moreover Chantal notices the source of the red light: when Mr. C first looks down at the phone, Chantal looks off into the distance and when she reaches a spot where the light might be coming from, her expression turns from normal to an acknowledging smile, as if she sees something-someone and is amused-informed by it(something like: hah, how about that, they are going to get him, and even looks to be trying to take instruction from it at one point, the light then turns off and Chantal tries to act normal again for Mr. C).  Probably Chantal and Hutch are also working with, or at least not opposing, people trying to get rid of Mr. C(Jeffries and Ray, Warden, maybe others) and are thus not loyal to Mr. C alone.

And I do think this light is like the green one Dougie had before, they are something like 'gazes' which represent how the bearer of that gaze is relating to reality, how they seek to fix some problems in reality, what they lack in reality; they connect to the 'red room'-lodges, giving them the ability to penetrate/change reality based on how these gazes/tracking devices are included into it, see the secrets of the insurance fraud, etc, in the case of the green one(law/justice in reality, lacking it because of fraud); something like tracking devices that can see through to the main core-problem of a person or a situation in reality,get access to the most effective weakness, secret, etc., that threatens to unravel everything.  So there is a tracking device on this truck, someone wants to kill Mr. C, they lack his power and his access to BOB; also, Chantal and Hutch know about this plan and who it is that is planning it.  As to the meaning of the color red, probably the source of the light is seeking-desiring(Red) to take Mr. C's spot, accumulate his power/money and his cooperation with BOB.  For these 'mafia types' desire-accumulation is secured by eliminating competitors, like when the cowardly Vegas guy saw the red light on his computer, he took out the papers calling for the killing of that 'criminal' woman and Dougie by Ike.

Posted by: Murat Erol Özkan

Probably Chantal and Hutch are also working with, or at least not opposing, people trying to get rid of Mr. C(Jeffries and Ray, Warden, maybe others) and are thus not loyal to Mr. C alone.

This is interesting considering that Ray said on the phone he knew where Mr. C was going and he would be waiting for him there. Now we didn't see Ray in last episode, so either the place where Chantal and Hutch were was just a stop-over and not that destination or there's a possibility he got there before DoppelDale and left instructions for Chantal and Hutch.

The look off the left into the distance that Chantal gives when Mr. C tells Hutch "remember this" seems too deliberate.  I like the idea of Ray, hadn't thought of that when I first noticed the light. I think it would be hard for her or both of them to play it cool, especially after what Chantal could infer happened to Darya.  They don't come across as very capable of such scheming, especially Hutch.  It would be a nice if they are secretly hoping to be rid of him and willing to aid and abet it.