Random signatures appearing

Hi,

Several members on my forum (www.halodog.com or dofgforums.niceboard.com) have come to me and advised that random signatures are appearing in their profile and posts. They did not add these signatures to their profiles on their own. As one of the Admin on our forums, I certainly did not add these signatures nor did the other Admin. Any comments on how this is happening or how we can fix this problem would be appreciated.

Thank you.