Just a guess (Chrome browser - menu - More Tools - view source) CTRL+F search for font = :
<span class="smalltext" style="display: inline; visibility: visible; font-family: Verdana, Arial, sans-serif;"><a href="http://www.hard-light.net/forums/index.php?action=credits" title="Simple Machines Forum" target="_blank" class="new_win">SMF 2.0.8</a> |
EDIT:
No font specified, followed by Verdana specified, followed by Arial:
testabcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
testabcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
testabcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
EDIT2: Means it's Verdana