Doesn't matter if they "copyrighted" their icons or not..
Basically, anything anyone creates, be it writing, code, or graphics of any kind, is automatically copyright them, regardless of whether they register that fact or not. Even this post, were you to reproduce it somewhere out of context without my permission, could be considered an infringement of copyright law.
If you'd like me to go into more detail about copyright law (I read up a lot on this), I will, but suffice it to say, that no, you can't take and use anyone elses images, unless they explicitely say so.
