it's a kind of message board slang - pretty much only used on these JA boards - that came out of an incorrect interpretation of what people THINK is Jamaican patois. it's a huge pet peeve of mine, for years now... "reach" is not a noun, and isn't used as a noun in patois either... patois speakers say something like "call me when you reach" - a verb.
If you replace 'reach' in any sentence with the word 'arrive', and see whether or not it makes any sense, that's what will tell you if it's being used correctly - either in speaky-spokey or patois.