How can you tell if a site is a template?

[Vincent]

How can you tell if a website if an existing template or it's built from scratch? This is assuming it's not stated on the site. Say a site looks like a wordpress site, but it doesn't say "powered by wordpress" or a forum doesn't say "powered by vBulletin" though it looks like one. Is there a way to know for sure?

 

[namestrands]

Check the source code