Phones have displaced paper money and credit cards as the preferred way to pay for a bill at the end of a meal. The trouble is, how does the waiter know when you're ready to pay?

The meal was delicious. The service, excellent. The waiter asks if you want dessert, but you decline... and feeling somewhat guilty you hurriedly justify this rebuke by explaining how you over-ordered one too many sides, are ready to burst, and couldn't possibly have room for sticky toffee pudding, but honestly, the food was delicious. The waiter brings over the bill, in a black rectangular wallet, and walks away.

We're now faced with a dilemma. How does the waiter know when we're ready to pay? For generations, the accepted signal was a banknote, and then a credit card, poking out of that said rectangular black wallet. In the age of Apple Pay, this vital signal has been lost. I've tried laying my phone over the receipt, but it just doesn't work.

This mutually agreed upon non-verbal signal is for the waiter's benefit as much as our own. People can be funny about restaurant bills - everyone has their own way of doing it, and it can be awkward to walk up to a table when Dave is still arguing with Sally & Val over whether that bottle of Pinot Noir should be split equally when Dave only drank a pint of Guiness.

So how do we solve the problem? I propose the most low-tech solution possible (please save us from another app or QR code). The bill should arrive with a card, red on one side, green on the other. The bill arrives with red facing upwards. When you want to signal that you're ready to pay, you turn it over. A solution so simple it almost guarantees that it won't be implemented. So for now I will resort to rather limply trying to catch a passing waiter's eye.