This question is probably off-topic because it's really not about copyright, let alone open source. However, the reason why deserves an explanation.
First, a quick primer: copyright and trademarks are different types of IP. Copyright protects creative works, and trademarks protect brand identities. Logos, being simple and recognisable, can sometimes be so simple that they cannot be copyrighted, but this has no bearing on whether it is trademarkable, which is determined by other facts - like whether it's a generic term.
If you decide to trademark your logo, it's best that you do this with a trademark lawyer, and possibly create a trademark usage policy, if you want others to use your trademarks. OSI for example lets other people use their logos if they meet their usage guidelines. If you read that document though, it would seem much more restrictive than typical open source licenses. This is because copyright is different to trademarks. A "free/open trademark license" is an oxymoron, since trademarks intend to protect identity, and not enforcing trademarks will often lead to them being declared invalid. It's this "use it or lose it" property that leads to open source projects like Mozilla to restrictively protect their trademarks, leading to products like Iceweasel.
Typical trademark licenses are quite specific; they usually specify a licensee and the types of activities allowed under the license. For example, LEGO licenses Star Wars trademarks from Lucasfilm in order to sell specific product lines meeting Lucasfilm's requirements (and nothing else).
So for now, I don't feel there's any need to do anything about your trademarks. You only need to take specific action if:
- You are large and engage in a lot of commercial activity, and therefore need to protect your brand identity
- You have specific licensees in mind
- You are an organisation like OSI or GNU, who would like their logos used by many third parties
Nevertheless, if you use an open (copyright) license for your logo, it lets other people freely derive the logo, as long as it doesn't end up too similar to your own.