I use this script at the bottom of each page. By inserting the code during 'Edit Page Layout', it is automatically inserted into each page. It's a little tricky because currently (as of version 2.7) you cannot create or insert a web gem while working in the 'Edit Page Layout' . So you have to use the Trellix Pass Thru technique!
Source code:
<SCRIPT LANGUAGE="Javascript">
<!--
document.write("<font size=1>This page last modified on: ");