displaying category and subject posts

I’m not sure if I get you right, but if so, this will solve your problem:

<?php
    $classes = array();

    $subjects =  get_the_terms( get_the_ID(), 'subject' ); 
    $categories = get_the_terms( get_the_ID(), 'category');  

    if ( count($terms) > 1 ) {
        $classes[] = "reset";
    } else {
        foreach ($subjects as $term ) { 
            $classes[] = $term->slug;
        }
    }

    $title_terms = ( count($subjects) ) ? $subjects : $categories;
?>
<div class="columns small-12 ">
    <div class="single-title <?php echo implode($classes, ' '); ?>">
        <h2><?php
            if ( count($title_terms) > 0 ) {
                echo $title_terms[0]->name;
                /* Or change it to this, if you want to display all of terms
                foreach ($title_terms as $term) {
                    echo $term->name;
                }
                */
            }
        ?></h2>
        <hr/>
    </div>
</div>