Well then, I can tell you why it won't work in signatures; html doesn't seem to be enabled for use in signatures (at least thats how it sounds).
A UBBCode varient would be:
[url=skype:outdoorking?call][img]http://mystatus.skype.com/bigclassic/outdoorking[/img][/url]
Though it won't work for several reasons:
1. URL isn't formed properly, so you'd have to hack at the URL ubbcode.
2. The image code doens't have a valid image identifier (.jpg, .jpeg, .gif, etc)
So, a test:
skype:outdoorking?call