Any professional who travels regularly knows that time zones can play havoc with communications. In order to help keep you from replying to people in the middle of (their) night, Gmail Labs now lets you see the time zone from which emails are sent.Google software engineer Marcin Brodziak opens his blog post about Sender Time Zone with an amusing anecdote.

Aside from perhaps waking up your significant other, it would probably be even worse to wake up your boss, or a business partner, at the wrong time. Enter Sender Time Zone.

With Sender Time Zone enabled (via Gmail Labs), Gmail adds some simple icons to emails that give you a visual reference to who might or might not be awake and available.

When it is between 9 am and 6 pm in the sender's time zone, you'll see a green icon next to their emails. If it is the middle of the night for the sender of an email, it will show a red icon, indicating to stop (or at least think twice) before calling.

You can also see more details, such as the exact time the person sent the email in their time zone and what time it is for them if you click the "show more details" link.

With Sender Time Zone enabled, you have one more weapon in your arsenal of Internet communications.