Who are the "Visitors" in the chapter 5 Solitude?

I don't believe we are ever apprised of exactly who the visitor was; the text reads.....

"When I return to my house I find that visitors have been there and left their cards, either a bunch of flowers, or a wreath of evergreen, or a name in pencil on a yellow walnut leaf or a chip. They who come rarely to the woods take some little piece of the forest into their hands to play with by the way, which they leave, either intentionally or accidentally. One has peeled a willow wand, woven it into a ring, and dropped it on my table. I could always tell if visitors had called in my absence, either by the bended twigs or grass, or the print of their shoes, and generally of what sex or age or quality they were by some slight trace left, as a flower dropped, or a bunch of grass plucked and thrown away, even as far off as the railroad, half a mile distant, or by the lingering odor of a cigar or pipe. Nay, I was frequently notified of the passage of a traveller along the highway sixty rods off by the scent of his pipe."