I think this all turns on, did the original author assert "Addtional Terms" under GPL v3 7e:
e) Declining to grant rights under trademark law for use of some trade names, trademarks, or service marks; or
If he did not, it would appear to this non-lawyer that he released the icon and branding under the GPL.
The author does not have to assert those additional terms to have trademark protection, because the law provides for that by default, and the GPL v3 does not have a trademark grant clause.
GPL v3 e7 means that, if for whatever reason, you do explicitly disclaim trademark grants, it does not violate or invalidate the copyright license.