Actually, MacLowlife, I normally carry those cotton handkerchiefs in the front, left pocket of my trousers, or more often overalls, especially in my role as scarecrow.

I do have a few set aside for use with suit jackets. I would really rather have silk pocket-squares in the breast pocket of a jacket, though. I would still carry a few cotton ones hidden inside other pockets, and back in the day, in the sporran.

And what of the handkerchief in the sleeve of one's jacket?