It was windy and cool enough for a topcoat the other day and out came the covert coat. As usual the chest looked a little bare so a silk square went into the breast pocket (a red carnation would have done the trick but none were handy).
Pocket squares in outercoat pockets are mildly controversial of course. Even HRH the Prince of Wales, diligent pocket square in suit jacket person that he is, leaves his outercoat breast pockets empty. On the other hand, he often has a flower or ribbon in his left lapel, and that serves the same purpose of adding some visual interest to the upper chest area.
Now there is still a school of thought that says that a man should never wear a handkerchief in the breast pocket of a city suit, let alone an outercoat, reserving them for the country (I believe this is a holdover from the frock coat era when city jackets had no breast pockets). Other men argue that where there is a breast pocket, there should always be a handkerchief.
Men who find controversy a thing to be avoided can obtain a ready supply of red carnations and ignore the handkerchief question of course, thereby securing all the style without any of the controversy. But given the effort associated with a greenhouse in winter, I will stick with silk.