How do you like your moss? Rare, deep fried, on a bun?

Actually, you won't find any moss at Mos Burger, which is probaby a good thing. Mos Burger is a fast food hamburger restaurant that bills itself as "Fine Japanese Burger and Coffee". Priced a little higher than McDonalds, it positions itself as better tasting hamburger, but that is for each person to decide. Standard "Mos Burgers" are burgers with a sloppy joe effect, covered in a thick chunky sauce. There are a variety of interesting things on the menu including burgers with rice patties instead of buns. Pretty tasty, though keeping the rice patties from crumbling when you eat the burger can be tricky for novices. The updated menu can be found at the Mos Burger site (in Japanese, but non-Japanese speakers can look at the pictures and let their imagination run wild)

So what does Mos in Mos Burger mean? Several theories could be put together but here is a sign to give an idea.