How can I tell if it’s working with Cloudflare CDN?

I went through the steps of adding my cloudflare api key and stuff to the CDN setting. But how can I actually tell if it’s working? I watched a video on youtube of someone setting up a differnet CDN provider. And at the end he visited the website, viewed the page source, and showed that it’s working because the URLs to all the assets had the CDN url at the beginning. I don’t see that with my site. Please advise, thanks!