I often see rsrsrs in emails or on the internet. From context, I'm guessing it should mean something like "lol", which is thought to be an acronym of "laughing out loud". But I'm not sure whether rs is an acronym or an abbreviation (maybe of some form of the verb rir), or simply intended to represent the sound of someone laughing or something else entirely.
So, what's the meaning and origin of rsrsrs?