I added the watermark tag to these three images because there's the signature at the bottom right of each of them. While it is very small and not disruptive, I still figured it'd be worthwhile to tag it... If anyone feels otherwise, please feel free to remove it.
No, a watermark is different from an artist's signature. A watermark is a disruptive overlay put on top of the picture to make it harder to steal and use for something. This doesn't interfere with the picture at all.