Often there is no way. Sometimes you may see it if you look at the HTML code, as some CMS list their titles in the meta tags. But you are not required to do this.
If you are interested in a particular site, you should contact the site owner and ask.
most of the time, in the footer it will be disclosed, but some webmasters edit it, so you will have to find it in the meta tags. if its not there, then there is no easy way to find it.
however, sometimes if you check the site in archives.org you can find earlier versions of the site, and sometimes you will find the cms disclosed in the footer in the earlier versions of the site.
Actually, there are tools that automate this process. Guess CMS/Software detector does this, for example. It uses some sort of finger printing based on url structure, css used, headers, and so on. It doesn’t depend on “meta generators” or footers that explicitly define the software used.
vldr
The Guess CMS detector isn’t really working good. It couldnt find ouf my own website was running WP3.0 beta. Or im just a really cool coder suddenly =)
