I have attached the Image here.
It is because anti-aliasing is on. Open up your Radeon’s Catalysts Control settings. You need to set the graphics settings for Unity. Turn off Anti-aliasing.
Same thing for anyone with the same problem who has NVidia (NVidia control panel, turn off anti-aliasing for Unity).
What does text look like if put a text box on a Canvas (assuming you’re using 4.6) and then try different fonts?
The font on the taskbar isn’t affected as screenname_taken pointed out and the Font looks different for that.
Never seen anything like it but it could just be a font issue if the Unity only uses one font for everything other than the Menus at the top.