The answer is no, tenants do not have to sign s.21, but it helps to obtain proof that they have been issued, i.e. a witness. For the first 10 months of their rental, everything was perfect and the rent was paid on time, but just before Christmas 2013, they went on a family vacation to Florida – mom, dad and the 4 kids and somehow forgot to pay the rent this month. They managed to pay 3 weeks later, but it seems that they never recovered from these massive expenses, their rent being late since. .