Iconic buildings can be landmarks for sure. Think of the Guggenheim museum in New York or the Opera House in Sydney.
But is it possible to register this building as a 3D trademark? A trademark must be capable to distinguish products and services from other companies. Can a building be distinctive? Thinking of the Eiffel Tower you see an endless range of souvenir products in the shape of the Eiffel Tower. Maybe too late for the Eiffel Tower, but if the Eiffel Tower was protected by trademarks in the name of the Eiffel Tower, the buyer would certainly assume that the products had their origin from the Eiffel Tower itself and not from one or some souvenir shop. So yes, a building can be a trademark and distinguish products and services.
This opinion is also shared by the EUIPO who has accepted the 7-star hotel Burj Al Arab and the Flatiron building as a trademark. Very important in these cases is that the building is significantly different from what already exists.
The stadium of the Athletic Club de Bilbao is now also registered as a trademark. The three-dimensional shape is registered with the logo of the Athletic Club de Bilbao. A former application of the 3D application without this logo was refused by the EUIPO. Despite the futuristic design of the stadium, the trademark didn’t significantly differ from already existing buildings, according to EUIPO. So, if you wish to trademark your building in 3D, choose for very distinctive design!