What did the wigged gentleman who was looking at the ceiling point out to the counsel, mr. stryve, on the piece of paper that he threw to him?

He probably pointed out that they looked similar because Stryver asked one of the two accusers after being given the note, if he had ever seen someone that looked like  Darnay before.
We can infer that it had something to do with their appearance.

And you could have mentioned that this is from "A Tale Of Two Cities"

Mickey Mouse is the name of his horse