Undefined control sequence: \signature

[d3adb5]

Even in a container running an image built with the provided Dockerfile, Pandoc (or better yet, pdflatex) hits the Undefined control sequence error on \signature.

I've tried adding graphicx to the list of packages installed by tlmgr, but it complains the package isn't present in the repository.

[wilkox]

I'm also getting this error. As mentioned here, adding:

---
documentclass: letter
...

to the YAML header seems to fix it.