In New England ballots are housed by municipalities. In a controversial election observers should drive by ballot facilities at night and on weekends as soon as you know there will be a recount, before it begins, to see whether cars are in the parking lot or the lights are on inside the facility. Take a video camera and videotape license plates, especially any cars with out-of-state plates, and any personnel you see coming and going, as well as any activity you can see inside the facility.
Examples: In New Hampshire's 2008 presidential primary election, I drove to the elections office in Londonderry the weekend before the recount, around 11 p.m. I didn't expect to see anyone there and was surprised to note that the parking area and building lights, normally on all night, had been turned out. Three cars were parked near the entrance to the elections office and lights inside were on.
Sham explanations: In a more bizarre situation, I went to the state archive building with election integrity advocate Paddy Shaffer. We asked about ballot delivery timelines and procedures, and were told that observers would not be permitted, and no cameras would be allowed in the area, because it might "violate the HIPAA rights" of local hospital residents who might be going for a stroll in the area. First, the ballots were originally scheduled to be delivered at night. Second, it was 14 degrees and the area was surrounded by 10 feet of snow, an odd choice for hospital patients to take a night time walk. Third, the hospital, nearly a mile away, was a secured-access state hospital housing mentally ill criminals. Shaffer advocated forcefully for the right to observe and videotape ballot chain of custody and eventually prevailed, at which point they decided not to deliver the ballots that night.