You should place a link because some people turn off signatures.
Personally, I'd get rid of the portal due to the forum being at a young stage. People want to get to the forum and post, but having something in the way may tell them to hit the back button.
I quite like the icons and the forum skin. It may be a little too white for some users, so you maybe should consider that.
Dark skins are 1990's. Brighter skins are more refreshing nowadays (based on many, many polls I've done within the past 3 years, including over 5000 users, where almost 75% preferred light coloured skins over dark skins)
Is that a custom skin, or a free downloaded one?
If it's a free downloadable skin, I'm not really sure what we look at to review, as it'll just be reviewing someone else's skin and your choice in forums and categories?
It's a nice skin though. Very clean and fresh. Needs a bit of colour adding to it, however. Give it a little bit of contrast.