Log in to your dashboard--> layout- -> Edit HTML, scroll to where you see this:-

<b:if cond='data:top.showAuthor'>
<data:top.authorLabel/> <data:post.author/>
</b:if>

Replace

<data:post.author/>

in the code with :

<a href='URL OF YOUR PROFILE'><img src='URL OF YOUR IMAGE' style='border:0'/></a>

Remember replace "URL OF YOUR PROFILE" and "URL OF YOUR IMAGE" with your details.

This gives you a signature at the bottom of your post and links it to your Blogger profile.