Gmail has added a Labs feature that lets you add your location to your email signature.
Developed by Marco Bonechi, a Google software engineer in his "20% time", the feature detects your location and appends the city region and country names to your signature.
The feature uses your public IP address to determine your location, so Bonehi warns it may not always be that accurate.
To make it more accurate users can equip their browser with a version of Gears that supports the location module so Gears can make use of Wi-Fi access point signals.
To try it, turn on "Location in Signature" from the Labs tab under Settings, then go to your signature preferences and tick the box next to "Append your location to the signature".