Its not always the programer...it is usally is the server that supports different sings.
it is better to use <?php ?> then <? ?>
Example 10-2. PHP Opening and Closing Tags
1. <?php echo 'if you want to serve XHTML or XML documents, do like this'; ?>
2. <script language="php">
echo 'some editors (like FrontPage) don\'t
like processing instructions';
3. <? echo 'this is the simplest, an SGML processing instruction'; ?>
<?= expression ?> This is a shortcut for "<? echo expression ?>"
4. <% echo 'You may optionally use ASP-style tags'; %>
<%= $variable; # This is a shortcut for "<% echo . . ." %>