Tooltips on Habré incorrectly display some characters. How to fix it?

Question

Habr

When you hover the mouse over the rating of a comment on Habré, a tooltip shows how many pluses and minuses the comment received. But instead of the symbols “↑” and “↓” I have just squares:

Should I change the system font in the system? If yes, how and on what? If not, how to fix it?
OS : Win7
Browser : Chrome

Answer 1

It seems to me that you have some kind of non-standard typeface in your tooltips, in which there are simply no necessary characters.
Did you install any user-styles?

win7, chrome 26

Answer 2

It's also a good idea to put the PT Sans font: in it, the number "3" and the letter "Z" clearly differ, which is the most useful property for small font sizes (which are usually used in tooltips).