Google has made the scribbles feature a part of the web based Gmail experience on iOS 4+, Android 3.1+ or Playbook platforms.
Google Scribbles is already part of the Gmail mobile app for the Apple iOS platform.
We hope that Google would add this feature in the native mobile app for the Android platform.
Android 3.1+ means that most Android smartphones in the market would not be able to make use of this new feature. You would need a Honeycomb based Tablet or an Ice Cream Sandwich based smartphone/Tablet.