you can always make an invoice and copy it and give it to someone in physical form, on a usb stick or printed as a QR code

but that's an invoice, the signed payment is a payment (payment request, actual payment)

lightning payments in this payer-initiated format are called "keysend" or "AMP" and have to be submitted to the payer's lightning node to work, meaning access to the LN RPC, which is not the usual situation for a lightning node (usually access to that RPC is private to the person using it, for security reasons). 

 Keysend is neat. how do you feel about the bolt12? 

 well, it's something that would also enable a kind of offline cheque payment mechanism too, that's its whole purpose 

 bolt 12 is like a comitment to pay that can be redeemed by the receiver

it's a very cool thing, that has only got contingent risk upon the closure of the channels the bolt 12 offer contains