**[-monochrome](http://www.imagemagick.org/Usage/quantize/#monochrome)** from ImageMagick is an option that uses some smart dithering, and makes the output much more visible than `-threshold` if you intend it for human consumption:

 convert -monochrome signature.png out.png

[![enter image description here][1]][1]

Does not make much difference for such a simple image, but for larger ones, it is striking:

- https://stackoverflow.com/questions/15861025/how-to-convert-an-image-to-1bit-px-binary-bitmap-with-imagemagick-or-rmagick
- https://askubuntu.com/questions/9868/convert-an-image-from-grayscale-to-binary
- https://superuser.com/questions/405686/how-to-convert-a-photo-to-a-black-and-white-image-by-imagemagick
- https://superuser.com/questions/75373/convert-color-photos-of-documents-to-good-black-and-white-bitonal-images

 [1]: https://i.sstatic.net/75qbU.png