Do you guys think it's better for SEs rankings of my sites if I post more in the Graphics & Multimedia DP forum section rather than anywhere else on DP? - because my sites are graphic design related. Or should I rather join a graphic design forum, as DP is a webmaster related forum.
I do not think it will matter for the SERPs but you might get more people who are interested in your sites and services.
I made it to page one (SERP) for many of the occult things I've placed in my sig here...though much of that has not resulted in a lot of digital point traffic. So yes, it'll help with SERP, but not so much for direct traffic.
He was not asking rather placing it in his signature would increase SERPs, he was asking if he posted mostly in the Graphics & Multimedia DP forum section would increase his SERPs. The signature in general does help with SERPs but that is not the question he was asking. For his particular type of service, posting in the specific forum may increase his traffic but it will not affect SERPs all that much.
I think you should do both, the more the merrier Posting on different forums is a good thing, and maybe you're right with the section. But when you post in topic about this stuff there will be enough keywords there aswell, although they might not be in that specific section