“CC 3.0” is not a license; it just means Creative Commons version 3.0. The type of license is usually marked by letters after the CC, e.g.: CC BY-SA 3.0.
My guess: I’m sure Jolla uses a permissive license for their icon design, because they’re interested in 3rd parties styling their icons accordingly, and those would fall under the same license.
Look for the actual license inside the SVG files themselves (they’re plain text).
(oops, /usr/share/icons/hicolor
features only PNG versions of the original, where did you get the SVGs from, esp. for apps?)
Do I understand you found those icons, and have not made the adaptations yourself?
In that case you should look for Licenses there.
Also see here