if you look at the source of the main page, you will see this tag on the source within the <head></head> tags. <meta name="generator" content="WordPress x.x.x" />
Using the page source it is almost always very easy to identify if it is a wordpress blog or not. As most people use all in one SEO, that is always a good way to check, but that is relying on the fact that the person who created the blog is using that plug in. Just open the page source, do a ctrl F, and search for the word "WordPress". That is always a dead giveaway.
search wp in source code..........................if you fount it then it is in wp.....................