good intelligence is your friend...as a former analyst of military radio communications I worked with the world's best Morse operators and foreign language specialists... unfortunately I don't have that resource today....as commented the social media sources are available, but I would rather go to the action arm of the local law enforcement, or fire rescue... even with encrypted or duplex (transmit on one frequency and receive on another) a few nights of playing with a frequency scanner can produce some clues, even if you are not able to actually understand the conversations

a change in the amount of radio traffic on a certain frequency is a clue... if you can associate actual incidents reported in a paper or on TV to previously observed increase of radio traffic, it may allow you to identify particular geographic areas covered by that frequency

a "broadcast" transmission without any response from other units typically reflects a high command authority... usually on a higher frequency

in the clear air to ground communications between air units and control

increase in local amateur radio communications... CERT communications

an area I am negligent in is not having a small portable AM/FM pocket radio with ear bud when away from the car, though I don't really spend time in large urban areas

don't forget the OODA loop

Observe....
Orient...
Decide....
Act...

a neutral color baseball cap, sunglasses, and if not out of place a hoodie helps you remain grey...