This one is into the weeds, even for me. If you haven’t watched Aunty Donna’s Big Ol’ House Of Fun, you should. Here’s a moment from episode five Night Time!.
Can you see it?
How about now?
The red dot on Mark’s sleeve?
It’s so incongruous, that it makes me think it has to be deliberate. It’s not mentioned, or called out, it’s just there.
A red dot.
I’m choosing to believe it’s a reference to this.