Google scans billions of URL’s every day and has a very sophisticated detection system. Most of the time it is accurate, so if your site is not showing and has been replaced with Google’s red Blacklist Screen, then the probability that the site has been affected is high.
Search for “Google Transparency Report” and run a quick check here to see what comes back.
You may have been contacted by your hosting provider with the news that your site runs malicious code. Generally a good indication that it does.
Your site users are getting redirected to spam pages elsewhere. Be grateful when a user alerts you to this and investigate fast.