Cold Temperature

An unnaturally cold air temperature is a symbol that a ghost is present. Lucy and the others are usually prepared for this, and they take constant temperature readings as a means of knowing that a ghost is near before they reach some crisis situation.

The Ghost Lights and DEPRAC

The ghost lights are installed and maintained by the city, which is a symbol that the ghosts that plague the city are recognized as a city-wide issue that the government has a responsibility to address. DEPRAC is a governmental department that oversees the agencies that are dealing with the ghost situation, which is another symbol that the ghost situation is so severe that the government is officially involved.

The Chains

Lockwood and Lucy forget to take the chains when they confront the ghost at Mrs. Hope's house, which is a symbol that they are not prepared...