With the release of V2.8.6 and V2.8.7, there can be an issue with background color of the signature field matching the background color of the page. It is there, the user can not see it. The new version grabs the wrapping div color.
To get around this issue add this to your frontend css (where: XXXX is a background color that makes sense on your site):
.cm-hipaa-form-signature-wrapper {color: XXXX}