Ps master, please come in. I wrote my signature with a blank sheet of paper, and then took it with a camera, ready to put my signature in my resume.
The simplest thing is to use the magic wand tool, adjust the tolerance and cancel the continuity. If the background color is uniform, click the background color to reverse the selection, if it is not uniform, click the signature part.
You can also use Filter-Extract to force the foreground color to be the signature color, then cover it with highlights and extract it.