Signal correlation vs Pearson correlation between signals
Thank robert bristow-johnson for the right question.
In my case signal coefficient shows a some level of similarity between noise-like signals because of appreciable mean values. That is as you compare two electrical noises with some direct voltage: of course they are as more similar as high equal direct voltage they have.
Since I need to compare specifically shapes, I should use Pearson method only (which "normalizes" data itself in terms of mean values).