See full post on BP-Tricks.com for full instructions http://wp.me/p2ZyW5-Jr

bp-notification-snippet.php

<?php
function bp_tricks_member_intro_text() { { ?>
    <script type='text/javascript'>
    jQuery( document ).ready(function() {
      // Member Directory Message
      if (!jQuery.cookie('member-alert-message')) {
          jQuery( "#member-welcome-message" ).show();
          jQuery("#expand-hidden").click(function() {
              jQuery( "#member-welcome-message" ).slideUp( "slow" );
              // set the cookie for 24 hours
              var date = new Date();
              date.setTime(date.getTime() + 1024 * 60 * 60 * 1000);
              jQuery.cookie('member-alert-message', true, { expires: date });
          });
      }
    });
    </script>

    <div id="member-welcome-message" class="intro-text">
    <div id="expand-hidden"><a href="#"><i class="fa fa-times"></i> Hide this Message</a></div>
    Hi! Welcome to our Member Directory! You can use our awesome search options to quickly find people in similar situations as you. Click on the "Show Search" buttons to see all the available search options! Have fun and make some new friend!  
    </div>
<?php }}
add_action('bp_before_directory_members_tabs','bp_tricks_member_intro_text', 1);
?>