I came across the expression in a book by Catherine O'Flynn "What was lost". Here is the paragraph.
She paid particular attention to unit 15 on the Langsdale Estate, where she had once witnessed what seemed to be an argument between two men. One man had a large moustache, the other wore sunglasses and no jacket on what had been a cold day – she'd thought they both looked of criminal character. After some deliberation and subsequent sightings of a large white van outside the unit, she had come to the conclusion that the two men were trafficking diamonds.
Is sighting the same as survelliance?