Thanks! It's the size for the most cheap (1$) "sponsorship" banner on TopWebComics.
Some other authors used these banners and said, that these banners worked good for them. But when I used my usual poster as a banner of this kind, I didn't get any significant increasing in visitors. So I've decided to try something more creative. This poor gif turned out to be very weird and unskilled... but well, at least it may draw an attention. I hope.