Care is needed by re-users of signature images. Signatures are still protected by forgery, counterfeiting, and other fraud laws, and may possibly be subject to trademark protection (even if no {{Trademark}} disclaimer has been applied). Lack of copyright protection is no defense if non-copyright laws are broken and, as always, it is for the re-user to ensure that the proposed re-use is allowed under local law.
Uploaded a work by John Thune for US Senator from https://wallpapers.com/images/hd/john-thune-photo-and-signature-gnniyklgi0l923lg.jpg with UploadWizard