If showing an up/down arrow next to a number, should the number still include a sign?

I have this display:

This is a kind of status update. The main number is shown large and in black, and underneath is an indication of whether or not this is more or less than yesterday. So this number above is 13 less than it was yesterday, or this number is 5 more than yesterday. It's not clickable. If it's zero, then it will just be a green zero with no arrow.

Given this kind of display, is it easier for a user to understand the meaning if I remove the negative sign? Or should it stay? At the moment, positive numbers are shown in green with an up arrow and no + sign.