Our military vets and members are probably very aware of term SALUTE. An acronym standing for Size Activity Location Unit Time Equipment.
How many? 25 guys. what are they doing: staging mobilization area. location: abandoned farm two miles east of the airport (lat/long or grid if available) Unit: who are they, police, national guard, looters? Time: of Observation not time of the report. Equipment: cargo trucks, AR/m-16 rifles? VHF/UHF portable radio?
Try your best to get as much information as possible. Report as soon as possible or at least in a timely manner and stay vigilant