Boromir claimed to 'see Frodo's mind', so perhaps Faramir could see Aragorn's.
On a more serious note, as was aforementioned, Ioreth's quippings were probably well known. Add that to his knowledge given by Frodo, his ability to see people's minds and intentions (handed down by his dear old pyromaniac dad), and the fact that Aragorn had somehow managed to pull him from the jaws of death, I'd say that there was a good chance that Faramir could put 27 and 34 together and come up with 61. (I refrain from 2+2 because it was slightly more complicated than that.) Or it was just the sort of thing that you 'know'.
Fea
|