With the new WordPress 4.4 embed feature the posts of your blog becomes embeddable in other WordPress sites, like you do when you embed Youtube videos or Twitter tweets.
Now to embed a post, simply paste the link in your WordPress editor, this is what comes out:
If you want to customize the output you can use the embed_template action hook to rewrite the html of the embed. If you simply want to change the icon in the bottom left corner of the embed. You can go to the Appearence menu and click on the Customize link, where you can select the Site Identity tab and upload an icon:
So the icon will be visibile in the bottom left corner and the WordPress icon will be removed.
Remove WordPress 4.4 embed post feature
If you don’t want that your posts are embedded in other sites, you can use a brand new plugin that is already out there and disable the embed feature.