Put the second line going all the way through it. Every single other currency symbol has the line going through it, because it's easier to draw 
$¥
$¥
Except bitcoin's?
BTC
I wanted to stay true to the one that's already known by most people.
My suggestion is for a 'reference design' which will naturally be reinterpreted by typeface designers
This might or might not work, depending on your installed fonts, but here for example is $ in Calibri $ and Courier New $