I do know how to do this . but the symbol seem to be look like a bit comma bent ..
A cartographic term I've seen for this sort of symbol is "herringbone". However, I'm not sure if ESRI has a pre-made font already for it.
Chris Donohue, GISP
In search for that I found and it shows it as a double arrowhead..
Alright... I just fixed and create my own symbol...
Here is the screenshot..
So you have a centipede here !!!!
Just kidding...
You asked for the name of the symbol...internally, we call it "Directional Flow Arrows", but I'm not sure if that is the "Official" name for the symbol you are seeking though....