Per the Help page here are instructions for hiding signatures.
If you want to hide the signatures of other members, log in to your forum account. Once you're logged in, click the Profile button found in the top menu bar and then on your profile page click the Edit Profile button. You'll then be taken to the Edit Profile & Settings page; once here, click the Settings tab. You'll now be taken to the Forum Preferences page where the second option listed will be for Show Signatures. If you want the signatures to display at the bottom of each post that is made on the forum, set this to Yes. Otherwise if you do not want any signature to be displayed below posts made on the forum, set this option to No. Once you have made your settings, click the Save Account Settings button found at the bottom of the forum. The changes you made will take effect immediately afterward.