It looks to me like those are small/thin rolls placed on the cake. For me that would be the easiest way to go :)
AYou can also try doing it by embossing with a ruler or triangle held vertically, but your fondant needs to be quite thick.
AI'd go with what kakeladi said. Fondant rolls... Dayti's idea with the ruler is surely easier / faster, but you would loose the round curves. Just an idea...why don't you pipe the rolls on? Need good piping skills, but that would combine both in one, fast and round.
I'm sure you can find some kind of item at the craft store to use as a type of impression mat in order to give you that effect without all that work.
You could buy a "ribbed smocking rolling pin" - there's a few different ones on the market. You might find it just as easy to indent with a ruler and gently wiggle back & forth to round out the edge a bit. I did this once to imitate wool on a ball of wool cake - it was sufficient, but I like the rolling pin tool better.