As I was leaving the MARTA (public transportation), a young guy who can easily be described as stereotypically gangsta said aloud, "As-Salamu Alaykum." I so was entranced with the Slayer album "South of Heaven" blasting in my ears that I barely realized he was speaking to me. I was taken aback. So much so that all I could do was make eye contact and nod; not even bow... simply nod. Only later did it occur to me that there is actually a reply to that greeting, "wa `Alaykum As-Salām," and that if I wasn't such a dumbass, I could have returned the courtesy. I was wearing my usual tan cargo pants, a long sleeved white shirt, and a beard that I've been growing since December, so maybe I was giving off a monk-ish vibe? I just don't know.
"As-Salāmu `Alaykum" is an Arabic language greeting used in both Muslim and Christian cultures. It means "Peace be upon you." The traditional response is "wa `Alaykum As-Salām", meaning "and on you be peace".
This type of greeting is common in the Middle East; it is similar to the Hebrew greeting of "shalom aleichem," meaning "Peace be upon you". The appropriate response is "Aleichem shalom".