Having either a logo or insignia would imply that you are representing a group, and therefore all actions adhere to the groups' standards.
You probably don't actually want this.
[smallcaps]That is, you don't want me tracking you down over NOT following standards.[/smallcaps]
Anyways.
Linking banners, however, might be considered, if they have good graphical quality & composition. And, of course, are consistent over standard sizes.
Which would be:
88px x 31px
200px x 40px
468px x 60px