Varda's Sickle blazes white in the midnight sky as Gandalf and Pippin fly southwards.
Seven stars above, as seven beacons burn below… The wizard's thoughts race along with Shadowfax. The Steward sends for succour – knowing not his King will answer! In what condition will we find Minas Tirith? Does Denethor already grieve his son-and-heir? And how fares Faramir?
Among so many troubles, one nudges the corner of his mind. As he probed Pippin's mind for the palantír, behind the burning trace of Sauron's seeking, something… someone else, watching. How ran that rhyme? 'Tall ships and tall kings, three times three…'
I may be bending canon a bit with the suggestion that Gandalf might be able to sense, when he probed Pippin's mind after Pippin had looked into the palantir of Orthanc, something of Denethor watching through the palantir of Anor. The bit about the palantiri in Unfinished Tales says, on the one hand, that 'the Stones each called to each' but then adds later that '[Only] the surveyor using the Master Stone of Osgiliath could "eavesdrop." I don't think I'm suggesting that Gandalf could have communicated with Denethor directly, then, even 'via' Sauron; but that perhaps inadvertently Sauron had also left some shadow of Denethor's watching in Pippin's mind...