Section 5.3 seems to cover this as well. There is only a problem if, say, you use a similar logo and similar domain name.
That said, to the extent that we care about not being confused with mirrors and forks, we should perhaps consider using a well-defined customization of Vector (with some colors and other visual features that are not the same as the default MediaWiki install) on the core WM sites. Then there would be even less of a chance of any confusion; or of any possibly unintended trademark conflict.
SJ