I want to know if forum posting, forum signature and forum profile are still effective on Google Penguin?
most of them are nofollow. You will get exhausted and consume lots of time to find just one that allows do-follow links.
Plus at least forum profile links seem to have been heavily devalued by Google. I think forum marketing still works, but more in the sense that if you post valuable content in forums related to your niches you can gain "authority" in the niche, and drive referral traffic to your sites from the forum, rather than from an SEO / Linkjuice perspective.
Of course. Because forum posting is the best way to get so much back links. You must use High page rank and do follow Forums for best result.
Yes,Forum posting is still effective that increases traffic to your site. and moreover if the content is quality and unique it id definitely useful.post valuable contents to the forum.