I agree with the first response that much of what reasonable suspicion is is a question of the context in which it arises as an issue, and it is not clear to me what exactly you are looking for in the way of four sources.
The most important case on this issue is Terry v. Ohio, 392 U.S. 1 (1968), and it does not discuss four general sources of information officers can rely upon to have reasonable suspicion. If there is case law that has such a "list," I am not aware of it. Terry, like most cases of this nature, avoids going much beyond the facts of the case at hand. But we do know that a police who observed men walking in and out of a store 24 times and consulting in between were the source of reasonable suspicion in that particular case.
So, as best as I can tell, a person's movement might create reasonable suspicion, a person's interaction with others might create reasonable suspicion, a person's words might create reasonable suspicion, and a person's appearance might create reasonable suspicion.
I should also add that reasonable suspicion is a much lower level of justification that probable cause, which is something like "more likely than not." Reasonable suspicion has a much lower standard because the stakes are lower, a stop, as opposed to an arrest, and a frisk as opposed to a search. What happens as a result of a stop and a frisk can create a probable cause situation, but if the reasonable suspicion does not hold up, then the elements that create the probable cause situation are the "fruits of the poisonous tree," meaning that evidence gathered had no reasonable justification to begin with.