Mailchmp is a great service. I use it. Here's a CSS code to make it more obvious.

/* Mailchimp override */
#mc_embed_signup {
    background: #eee none repeat scroll 0 0 !important;
    padding: 3px;
    border: 1px solid #aaa;

#mc_embed_signup h2 {
   margin-top: 0px !important;


Why is this important? We'll it will attract attention and therefore this will increase the likelihood of a person joining your mailing list.

Of course you can customize the border, background etc.  You need to paste the CSS snippet above in the style.css file of your (child) theme.