"You could signal directly, such as an ATM receipt." Not sure what you mean here - are you saying 'show everybody the receipt'? That's not signalling, signalli

"You could signal directly, such as an ATM receipt." Not sure what you mean here - are you saying 'show everybody the receipt'? That's not signalling, signalling includes 'being socially acceptable', which talking about how money you have or walking around showing your ATM receipts certainly isn't.