see http://en.wikipedia.org/wiki/File:Gotpike.png what is missing is the actual copyright information on the logo. i could not find that on the pike site.
a simple page that clarifies that the pike logo is copyright by ida, all rights reserved (to make clear that it is not gpl like pike itself) would already be enough.
for more details we probably need to ask a wikipedia expert.
as for the actual license of the logo, we should consider pike icons in the source distribution which should be gpl.
my suggestion to make the logofiles itself gpl was mostly for simplicity, to not have to bother with a seperate license.
greetings, martin.