Signal Spam is described as 'provides email and web client tools to allow you to submit spam emails you have received. These spam emails are then analysed, categorised and added to a database of known abuse. ISP's can subscribe to this database for free to help filter out and block spam'. There are four alternatives to Signal Spam for Online / Web-based, Wordpress and Self-Hosted solutions. The best alternative is SpamCop, which is free. Other great apps like Signal Spam are StopForumSpam (Free), CleanTalk (Freemium) and Akismet (Free Personal).
Anti-Spam Features. CleanTalk protects your website from spam bots and spam in Comments, Orders, Widgets, Registrations, Bookings, And any custom web form, Contact Emails, Subscriptions, Checks the existing comments and users for spam.
Akismet checks your comments and contact form submissions against our global database of spam to prevent your site from publishing malicious content. You can review the comment spam it catches on your blog’s “Comments” admin screen.