"Hide Input Source Name" changes to "Show input source name" on every reboot, on Lion
Another thing you could try would be to lock ~/Library/Preferences/com.apple.menuextra.textinput.plist in Finder. (OS X performs atomic saves on preference files so chmod 600 wouldn't work.)

At least on my account the file contains just a ModeNameVisible key:

&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"&gt;
&lt;plist version="1.0"&gt;
&lt;dict&gt;
    &lt;key&gt;ModeNameVisible&lt;/key&gt;
    &lt;false/&gt;
&lt;/dict&gt;
&lt;/plist&gt;