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.
This question is a little bit vague because it doesn't specify what the situation is. You're asking specifically for four things, though, and so I am going to use drunk driving as an example. What four things can allow a police officer to have reasonable suspicion that someone might be driving under the influence?
- Driving in a way that violates motor vehicle laws-- if an officer observes someone driving in a way that breaks the law, such as weaving between lanes, driving excessively slow, etc, the officer can draw the conclusion that the operator may be impaired.
- Equipment problems or out of date tags -- if a vehicle has faults that affect its safety, such as burned out lights, or if the registration tags are out of date, the officer can be reasonably suspicious.
- Third-Party reports -- if someone else, such as Joe Otherdriver, calls in a report of a vehicle matching the description of yours, a case can be made for reasonable suspicion. This information has to be pretty credible, though, and the officer must have a justifiable belief that the car in question is the car that has been reported.
- Side of the road -- officer's are allowed reasonable suspicion of intoxication of the person's car is stopped on the side of the road, especially if the person in the stopped car is sleeping.
These are examples of four types of information that would create a situation whereby officers could assert a lawful suspicion of wrongdoing.