Gmail added a new lab feature which automatically detects and adds your location information in to email. This feature is developed by Marco Bonechi, Software Engineer at Google. This is an experimental Gmail Labs feature that detects your location and appends the city region and country names to your signature, like this:
You must have your signature enabled in order to activate this feature. To try it, turn on Location in Signature from the Labs tab under Settings, then go to your signature preferences and check the box next to "Append your location to the signature."
It'll use your public IP address to determine your location, so it may not always be that accurate. For example, if you're at Heathrow airport, IP detection may put you in Germany. If you want more accurate location detection, make sure your browser has a version of Gears that supports the location module. That way, Gears can make use of wi-fi access point signals to recognize that you're actually in London.
You'll always be able to disable the option or just delete your location from specific emails whenever you want.