yes, you can interact with Signal programmatically, and the company's main client is open source + the protocol has specs
You can sacrifice some accessibility of your website (eg. making it inaccessible to blind entities, or to anyone with a slow internet, etc) to try to stop scraping
You can also deploy various anti-bot services like Anubis which will make it more costly to crawl your site and should make most bots avoid it (again at the cost of some accessibility)