Pure CSS (without extra HTML markup) comment speech bubbles for SquareSpace blogs.

comment_flag_in.css

.journal-comment-area-wrapper .comment .signature:before { 
    font-size: 10px; 
    content: ''; 
    display: block; 
    height: 0; 
    width: 0; 
    border-right: 2em solid #666; 
    border-bottom: 2em solid #000;
    border-bottom: 2em solid transparent; 
    position: absolute; 
    right: 4em; 
    bottom: 4em; 
}