SIGNALSPAM 3.3.0 for Mac was available to download from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. We recommend checking the downloaded files with any free antivirus. This free Mac application is an intellectual property of VERIFROM SAS. The software lies within Internet & Network Tools, more precisely Browser extensions.
From the developer:
Signal Spam is a public-private partnership that allows Internet users to report anything they consider to be spam in their e-mail in order to then assign it to the public authority or professional who can best take the necessary action to combat the reported spam. This extension allows you to report an unsolicited e-mail from compatible webmails, including Gmail, Outlook.com, Live.com, Yahoo! Mail, SFR, Orange, Free, OVH, LaPoste.net, and AOL.
You may want to check out more software for Mac, such as PointerServer, KIDOZ or Delish, which might be related to SIGNALSPAM.