How to show category only if assigned

I’m trying to show the category assigned to search engine results, with the desired output as:

Posted in Category | Tags: Tag A, Tag B

Of course, I don’t want that text “Posted in” to appear if there is no category, and I don’t want the divider character either in that case. I’ve tried the following code, but it produces strange results:

<dl class="entryList">
		<?php while (have_posts()) : the_post(); ?>

		<dt id="post-<?php the_ID(); ?>"><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></a></dt>
		<dd class="postmetadata"><div class="asideBlock date"><?php the_time('F jS, Y') ?></div><?php the_excerpt() ?><?php if ( in_category( 'Advertising', 'Design', 'Web', 'Tools', 'Marketing', 'Branding' )) echo the_category('Posted in ',', ',' | '); ?><?php the_tags('Tags: ', ', ', '<br />'); ?> </dd>
		<?php endwhile; ?>
	</dl>

What am I doing wrong?