Apple Wallet has been an amazing channel for brands to engage with their customers and one of the features was allowing brands to promote their App at the back of their passes.
With the new iOS 9.3, if a brand integrates the App with the pass, the App icon will also appear on the bottom left of the front of the pass where previously was the share icon
If you tap on the icon one of two things will happen; if the App is already install it will automatically open, otherwise you will be directed to the App store to download the App.
Since the begging of Apple Wallet on the bottom left corner of the pass there was share icon. By tapping on that icon users were allowed to share their pass via message, mail or airdrop.
In iOS 9.3, and covered by previous point, the share icon has been removed and now appears on the back of the pass as a link right bellow the Automatic Updates and Suggest on Lock Screen.