Don’t do it, please. Signature is not part of artwork. It is an intrusive element which only purpose is to say “This is mine”. Sometimes the author takes the effort to hide it inside their work, making it part of it. I appreciate that but there is a better way.
In case of physical paintings it can be put on image border, if there is one, or on the backside of the paper. For digital paintings we have image metadata, be it XMP or one of the older formats. So just use that, because removing signature from artwork is not hard (and neural network powered tools make it even easier), therefore it does not make the image any more protected when compared to metadata information.