According to VocaLink:
"In June 2015, Zapp unveiled Pay by Bank app. This will be a universal symbol indicating to consumers that a retailer can receive a mobile payment directly from a bank app. Pay by Bank app is putting real time payments on mobile phones for the benefit of consumers.
Pay by Bank app will become the Zapp’s consumer facing brand from launch. It is the symbol that consumers will see and interact with and the one used by Zapp and its financial services and retail partners in their consumer marketing."
As per a previous post in this community Barclays have signed up to Pay by Bank (VocaLink's Pay By Bank app)