"We have not found what we sought," said one. "But what have we found?"
"Not Orcs," said another, releasing the hilt of his sword, which he had seized when he saw the glitter of Sting in Frodo's hand.
"Elves?" said a third, doubtfully.
"Nay! Not Elves," said the fourth, the tallest, and as it appeared the chief among them. "Elves do not walk in Ithilien in these days. And Elves are wondrous fair to look upon, or so 'tis said."
"Meaning we're not, I take you," said Sam. "Thank you kindly. And when you've finished discussing us, perhaps you'll say who you are, and why you can't let two tired travellers rest." (4.4.68-71)
It's a sign of how far Frodo and Sam have come from the Shire that they have found men who do not even recognize what they are. Hobbits are so out-of-the-way in terms of Middle-earth geography that the men of Gondor don't even know what they are looking at when they find them (rather like Treebeard with Merry and Pippin). And of course since Frodo and Sam are so wildly different from anyone Faramir and his men have ever encountered, the humans regard the hobbits with a healthy dose of skepticism.