Which of the following is an indicator of a criminal or terrorist act involving explosives?

The theft of explosives serves as a clear indicator of a potential criminal or terrorist act because it signifies an unlawful acquisition of materials that could be used to construct or deploy an explosive device. When explosives are stolen, it raises concern about their intended use, particularly if they are taken from locations such as construction sites, military installations, or storage facilities where such materials are properly regulated. The illicit nature of obtaining explosives suggests premeditation and potential malicious intent that aligns with behaviors commonly associated with criminal activities or terrorism.

While excessive advertising of fireworks or increased community events may raise eyebrows regarding local safety and might reflect community engagement, they do not directly link to the intent or planning of a criminal act involving explosives. Surveillance footage could provide useful evidence in investigations but, by itself, does not indicate an act without context to what is being observed. Therefore, the theft of explosives stands out as a more definitive sign of a possible threat related to explosives, making it the most relevant indicator among the provided options.