The user should be able to add custom emblems.
Moving to 0.4.0rc1.
Moving to 0.5.0rc2.
Moving to 1.0.0final.
Is this bug resolved ? 1.0.1 is out and it does not seem so. (I found a link to this bug here : http://thunar.xfce.org/pwiki/documentation/faq)
You can manually add emblems as well. What you need to do is adding images in your theme, in /usr/share/icons/mytheme or ~/.icons/mytheme under the folder emblems available for each size. You also need to restart thunar to let them in.
If you have Nautilus installed as well then you can add icons in it and they will show up in Thunar as well.