Android's always given developers more elbow room when it comes to hacking into its mobile OS. Here's a case in point: putting a connection speed indicator in the Android status bar (and notification tray).
The app we're going to use for the job is Internet Speed Meter Lite though there are alternatives out there. It won't cost you anything and is ad-free too, but if you decide to upgrade to the pro version, then you get an extra notification dialog, more statistics, theme support, and smarter notifications.
Once you've got the app installed on your smartphone or tablet, your current download speed (wi-fi or cellular) appears on the status bar and in the notification drawer as well. Tap on the app to see daily stats and set preferences -- it's possible to display both upload and download speeds, hide the lock screen notification, and more.