It indicates the premises is part of the 'Nette Toilette' (Nice Toilet) scheme, and you can go in and use the convenience without necessarily feeling you have to buy something.
What happens is the premises gets a monthly payment from the local authority to allow its facilities to be used by the general public and not just customers.
The network, launched in 2000, now has 210 member cities in Germany and is also spreading into Switzerland.
As an example, the City of Bremen pays out some €150,000 a year to participating premises and gets in return a system of public conveniences that would otherwise cost them €1.1m a year to operate.
The cost includes a relatively small payment to the private company that runs the branding, which also operates a website where you can find the nearest participating restroom..
Could work here, couldn't it?
