It is standard practice in Switzerland to include a red or orange payment slip with every bill. You need this slip to pay the bill. As a foreign newcomer in Switzerland it is the first time that you see this kind of payment slips as it is used in Switzerland only.
The bank UBS made a brochure Payment solutions for individual clients in Switzerland to give you some practical tips and useful information regarding day-to-day payment solutions in Switzerland. On pages 8 and 9 they explain how to pay with the payment slips.