It all depends on the frequency and what you are hearing. When I come across something new, I first do a TAFL/Spectrum Direct search to see if there's anything associated. In 80 percent of the cases, this will usually answer what it is, unless it is unlisted. Then it's only a bit of detective work. Depending on the frequency, repeater offsets are generally pretty standard. If I seek on the input or reverse frequency and hear nothing, I know that it is simplex. If there's a nearby control channel or data bursts associated with LTR for example, I search for other trunk associated frequencies and channels. As for AM/FM/NFM/WFM, it is usually FM, but a quick press of the button or a glance a spectrum display will show you/enable you to hear what it is.