There are no references to the footprints (as far as I'm aware) in any other EU properties, but the scorched earth circle is mentioned in the official novelisation. The two council workers; Javy and Ben return to the park on several occasions in the hopes of getting another glimpse of their elusive vision. When the ship finally takes off, leaving only a burn-mark on the ground they decide not to tell anyone about it, for fear of being dismissed as cranks.
"I saw it," Javy said. "I saw its shadow, anyway." "But, I mean, we would of seen it and we would of been able to show it to other people. To a reporter, maybe, and they'd write us up in a book and maybe we'd get on Johnny Carson." He brightened. "Maybe if we show them the burned place-"
"Maybe if we show them the burned place, they'll arrest us for arson. Or they'll write us up as a couple of nut cases," Javy said. "And maybe they'd be right. We don't have any proof. A burned place and a shadow."
"I'm really sorry," Ben said again, downcast. "Don't be, Ben, it's okay, honest."
"I'd be mad, if I were you."
"Maybe I ought to be," Javy said. "Except ... " He hesitated, not sure he wanted to say it out 'loud before he was certain it was true.
What the hell. Telling Ben the story had always worked before. Javy grinned. "I figured out how to end my novel," he said.