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 ;)
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...Here is a summary of copyright laws for logos in the USA http://info.legalzoom.com/close-can-logo-not-copyright-infringement-27335.html
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 :)