The sign isn't a new one but it is a necessary one. Each year the owners of a restaurant on the Coll de Soller put up a blackboard with a notice asking cyclists not to relieve themselves in the restaurant's grounds.
The Coll de Soller provides one of the most popular climbs for cyclists, and of all the thousands who take the route some need somewhere 'to go'. This is a problem the restaurant has had to contend with for several years; hence the sign.
In three languages - Spanish, English and German - it makes clear that the grounds are not "a public toilet". The owners don't want unpleasant smells or unpleasant deposits just a few metres from the entrance and the terrace.
The sign does actually have an impact. But the cyclists then have to look for somewhere else.