Our branded travel pass holder each has the message 'Give me more time' on the front and an explanation that you stammer on the back. Handy for that time when dealing with the ticket desk, salesperson, bar person or waiter who doesn't understand why you are blocking or stammering.
We've got some for adults (where the suggestion might be that you are drunk) and for children & young people. Buy a colour that suits you, or go the whole hog and buy a pack of three. Each card holder includes an 'I Stammer' card. The cards can also be bought separately, see here.
*UPDATE: as we're working from home right now, we aren't able to come into the office and send items out, so our shop is suspended for the time being. If you desperately want a physical item/s, email firstname.lastname@example.org