When travelling on the M56 just by Helsby hill, there are signs painted on the road saying "keep two chevrons apart". Why is it only listed there and nowhere else on the motorway as far as I can tell? It's always puzzled me

Could be many reasons

That bit was an accident blackspot
It's a straight unlit piece of road, so could be there to keep drivers occupied
The Runcorn turn off is next which gets busy so could be again to get drivers paying attention for ques
Or could just be a random placement

People should know what the chevrons are for anyway, I'm puzzled there are signs telling people.

I've always thought the "2 chevrons apart" signs are a bit odd. Surely the distance to be kept between 2 cars must depend on their speeds? Imagine if the rule was followed during periods of high congestion.

Should the rule be interpreted as "2 chevrons apart at 70 mph"?

If I remember it's referenced in the highway code.
It's the same rule as no undertaking?

Common sense applies with slow speeds like in a que You couldn't keep 2 cheverons apart in a que as someone else would just drive into you're 2 cheveron space. Just like your not allowed to undertake, but in a que at 2mph your going to move with the flow.

Common sense applies as it's saftey in mind.

There doesn't appear to be any reference to these chevrons in the current Highway Code, although I'm sure there has been previously.
There is no law against passing on the left (undertaking), but guess who will get the blame if there's an accident.
Rule 268 of the Highway Code says "Do not overtake on the left, or move to a lane on your left to overtake..." This is advice, not a prohibition; prohibitions always start with "You must not".

Particularly bad stretch of road when the sun is low in the sky especially travelling in welsh direction. Think the idea of chevrons to keep traffic spaced is to help keep the traffic flowing rather than people braking all the time.

I understand that it's a reminder for people to keep a safe distance from one another, it ought to be that way on all roads 100% of the time in my opinion but I've never seen it on any other stretch of motorway (not that I travel on that many of them).
Thanks for the answers though

I also noticed while driving on this stretch last night that there is no crash barrier on the hard shoulder side Manchester bound so again, could be to keep drivers paying attention