Final answer:
Indicators of an explosive/incendiary attack include unusual security measures, abandoned spray devices, and unusually colored smoke or flames.
Step-by-step explanation:
Indicators of an explosive/incendiary attack may include unusual security measures, such as increased police presence, security checkpoints, or restricted access to certain areas. Another indicator could be the discovery of abandoned spray devices, which could be used to disperse flammable or explosive substances. Additionally, unusually colored smoke or flames may suggest the presence of chemicals or materials used in explosive devices.