How to get around forum signature links?

First off, most forum signature links are nofollow, so they would have no effect on SEO, positive or negative.

There probably are a few forums left out there with followed link profiles. It is HIGHLY UNLIKELY that removing them is going to help you link better. Google places little to no value on any link you can place yourself, such as forum signature links (or any forum links, for that matter). Of course, they won't help you rank, either. If you have a manual penalty message in your Search Console, then maybe eliminating them would help (you'd have to have a ton of them and a link profile made up mostly of those and other easy to place links to get penalized for them, though).

I'd sure like to see those "case studies". I can't imagine they are from a reputable place. Either that, or you are totally misinterpreting the study.

The benefit of a forum is not any SEO value of a link. It is becoming a respected member of that forum and then having some people purchase from your site because of your reputation - not because of any rankings boost the link gave your site (which is none).

Most of the forum members overlooked one of the most important benefits in joining forums which is to gain knowledge and experience from your favorite field.

You didn't rank with forum sigs so you didn't lose rank because of forum sigs.

Avoid whoever made the case studies.

Forum links are useful for SEO & It can create a trail of links for people to follow your site.

Honestly, if you want to test this and do your own case study, just remove the links under your forum settings, do a Fetch as Google, and wait a few weeks to see what happens.

As others have already pointed out, I'm fairly certain you won't see any significant change at all. The only SEO metrics that this is going to have any chance of influencing are your anchor text ratios and follow versus nofollow ratio.

Backlinks from forum signatures do not pass SEO value.