[nunobrito]

You seem to be unaware that Portuguese trade was happening in China (Macau) and the main hub connecting to European Portugal was based at India.

Those boxes wouldn't write "chá" because they often contained cinnamon, sugar and many other valueable spices. The point wasn't advertising the specific content, but more to remember that those specific boxes should not be placed on the bottom of the boat, where water would spoil the contents.