Here’s a tip submitted to us by a reader, Steve: You can customize the menubar clock (upper right corner) to include more than just the time, but Apple doesn’t put the option in the Date & Time prefs. Instead, launch the System Preferences, and visit the “Internationl” preference pane, followed by the ‘Formats’ tab… next click the “Customize” button in the Times pane. Here you can alter the appearance of the Time format, add the date (in a format you specify), or add a custom message.

Depending on what version of OS X you are running, the exact parameters might be a little different but it’s the same concept. To show the Date, extract the Date info from the International -> Formats -> Dates pane. You just hit the customize button, then paste the Items you want to show. You can even add in static text if you want to, like OSXDAILY Rules! or something to that effect.

The end result can really be anything you want, you can see what I did quickly to demonstrate the effect.

Submitted by: Steve
Source: Howto: Date & Time in the Menubar