© means copyrighted tracks. These are commissioned or private tracks that may not be used for anything beyond personal use.
CC-BY means tracks released under a Creative Commons Attribution 2.0 Generic license. These tracks are either completely finished or as finished as they’re going to get (i.e. abandoned). They may be used in any way the license allows.
WIP means unfinished tracks that I will get back to working on when time permits. These may not be used in any public projects, but using them for personal stuff is fine, e.g. as placeholders in a game you’re developing.