Inside a previous publish ( I requested the way i would start getting my header echo a div when the user loaded a URL with /blog within the header.

Things I did not consider, was that I'm not going the div to show if it is not only got /blog within the url, but when its any blog publish, not only the index page from the blogs.

How do you run a little of code from the header.php when the page I am searching at is really a blog publish?

You would employ the Wordpress functions is_single() and it is_page.

if(!is_single() && !is_page() && !is_home() && !is_archive())
/* This will not display for any post, page, the home page, or an archive.
 You can remove each is statement according to your needs */

For just posts, just use is_single, exactly the same for page, home, and archive.

The entire report on is_claims are available here. Here are a few others:

is_home() : Home Page
is_front_page :  Front Page
is_single() :  Single Post
is_admin() : Admin Panel
is_sticky() : Sticky Post
is_page() : Page

It has been lengthy since I have performed with wordpress however, you is capable of a great deal with while using conditional tags:

Appears like is_single() might do what you would like. Eg:

if (!is_single())
    // display div