On the bottom of the page of that forum you will find two links that take you to their privacy policy and their terms of use. You agreed to it without reading it when you signed up.
In those two documents you'll find out just how much of your intarwebs rights you signed away. Did you know that if you post something on that forum, then copy it to post on another forum, it's a federal misdemeanor that carries a penalty up to and including 10 years in prison? Once you post anything... your picture, some text, anything, it becomes the sole property of the site to which you posted it. If you post your own recipe for apple pie, they own it. If the site admin makes your apple pie and thinks its the best on the planet, they have the right to publish it in a cookbook and make money off of it and not only can you not sue (there are arbitration clauses in the agreement as well), you can no longer disseminate that recipe as your own, and if they copyright it, they could technically sue you if you even MADE that pie again.
They also have access to everything you do. They don't just read your PMs, the AI reads your browser history, the other devices hooked to your network including your TV and what you watched on Netflix, your phone and it's history, and (depending on how your permissions are set up on your devices) even things you've said to your dog that were picked up by the microphone. Having said that, the details of how the AI uses that information are regulated. They just want to see that you were browsing for parts on Rock Auto so they can put an appropriate ad in the banner while you're visiting the forum.
Here is a selection or two from the Vertical Scope standard agreements for comparison. And yes, I promise no one but me actually reads these things.
If you do not agree with any of these terms, do not use this site.
You agree to grant to [forum website], VerticalScope and its subsidiaries, a non exclusive, royalty free, worldwide, irrevocable, perpetual license to reproduce, distribute, transmit, sublicense, create derivative works of, publicly display, publish and perform any materials and other information you submit to any public areas, chat rooms, bulletin boards, newsgroups or forums of [forum website] or which you provide by email or any other means to [forum website] and in any media now known or hereafter developed. Further, you grant to [forum website] the right to use your name and or user name in connection with the submitted materials and other information as well as in connection with all advertising, marketing and promotional material related thereto, together with use on any other VerticalScope Inc. web sites. You agree that you shall have no recourse against VerticalScope Inc. for any alleged or actual infringement or misappropriation of any proprietary right in your communications to [forum website]
You agree to grant to [website], VerticalScope and its subsidiaries, a non exclusive, royalty free, worldwide, irrevocable, perpetual license to reproduce, distribute, transmit, sublicense, create derivative works of, publicly display, publish and perform any materials and other information you submit to any public areas, chat rooms, bulletin boards, newsgroups or forums of [website] or which you provide by email or any other means to [website] and in any media now known or hereafter developed. Further, you grant to [website] the right to use your name and or user name in connection with the submitted materials and other information as well as in connection with all advertising, marketing and promotional material related thereto, together with use on any other VerticalScope Inc. web sites. You agree that you shall have no recourse against VerticalScope Inc. for any alleged or actual infringement or misappropriation of any proprietary right in your communications to [forum website]
Information we collect...
Transactional information: We may collect your name, contact information and payment card information when you purchase a product or service through our Site (such as a subscription or classified advertisement). Payments are processed by third-party payment processors (e.g., Stripe and Braintree), so please refer to the applicable processor’s terms and privacy policy for more information about how payment information is processed and stored.
Third Party Networks: If you use a third party network (including a social media account) to create an account on our Site, to log-in to our Site, or if you otherwise interact with a third party network through our Site (such as by using a plug-in), we will receive personal information from the third party network, such as your username, email address, gender, public profile information and any other information that you have agreed to share with us, whether explicitly or through your privacy settings. You should consult the respective privacy policies of these third party networks for information about their practices.
Geographic Location: We collect geographical location information if the Site you are using is location-enabled and your device transmits location data and/or your IP address. This enables us to provide location-specific information to you.
Usage Data: We may log information when you access and use our Sites. This may include your IP address, user-agent string, browser type, operating system, referral URLs, device information (e.g., device IDs), pages visited, links clicked, the requested URL, hardware settings, and search terms. See Cookies, tracking technologies and interest-based advertising below.
Information collected from cookies and similar technologies: We, our service providers and third party advertising partners also collect information about users of the Sites automatically using cookies and other tracking technologies. See Cookies, tracking technologies and interest-based advertising below.
Most modern web browsers provide the option to send a “do not track” signal to the websites you visit, indicating that you do not wish to be tracked. At this time, there is no generally accepted standard for how a website should respond to this signal, and we do not take any action in response to this signal.
Basically... we can do whatever we want and there's nothing you can do about it. This is just a few paragraphs from two large legal documents, both of which you agreed to when you signed up. You cannot sign up unless you agreed to these terms.