Search Engine Forums, SEO Forum

Between us speaking, in my opinion, it is obvious. Try to look for the answer to your question in google.com
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I think forum links are of high importance for getting a good rank in Google and other search engines and it will really help others to find your site with ease.

Yes, it can be harmful when you create a back links over a anchor text in forum signature then for sure the keyword will get over optimized.

Usual forum posting questions are-
Ways to generate backlinks
Social media
Ranking
Off page methods
black hat seo