A really good advice here:
Drizzy said:
PM Zise to report obtrusive or malicious ads. If it's not redirecting you to another webpage, redirecting to an app store or generally making it difficult to use the forum then just close and ignore it.
I tried browsing the forums both logged in and as a guest for a bit and nothing happened to me on my phone. The adverts that NB uses are banners visible in the sides of the site or down below. As a guest you might see these between posts as well. I don't know of any sort of redirect pub. And it never happened to me on NB and I don't think its supposed to happen.
Most likely its something installed on your phone without your knowledge. Happens a lot in Android and iOS phones with the default web security settings. I dunno the details but you should be able to quick search the web for solutions on how to protect your phone from such things.