Ok, no problem, copyright laws are kind of insane, especially because they are different in every country and if a lawsuit occurs and it goes to court either a judge or jury determines if a copyright violation has occurred. I doubt anyone would ever consider suing you over this logo just because a silhouette in it looks similar to another silhouette, but you never know there is all kinds of crazy people out there ;)
Here is a summary of copyright laws for logos in the USA http://info.legalzoom.com/close-can-logo-not-copyright-infringement-27335.html
The insane thing is even if you follow the law does not mean that someone in another country with different laws wont sue you for copyright infringement...
Yeah, you are completely right, these laws are quite complex.
To avoid all that stuff, I wrote in the description of the participant conditions that I wouldn't accept logos that include any type of third partie elements. The logo needs to be 100% yours, then nobody would ever face any kind of copyright issues - neither the designer nore the publisher :-) Sorry that I need to be that strict here...
Yes, no problem, thanks :)