Thanks for the replies!
Yup, Retro Mode did fix it. Interesting... Well, we are in the process of updating our website, so we'll look into this while we're at it.
Here's one of my posts where you can see my signature: http://www.potku.net/forum/viewtopic.php?f=29&t=20153&p=834402#p834402
In Retro Mode, it looks just like it should.
I switched the coding from Unicode UTF-8 to Automatic (after trying a few of the options). I still needs Retro Mode, though.