Commodities are evaluated by officials also (and often) just by appearance, smell etc. Or in some cases confirmed by lab tests. In some jurisdictions, just a suspicion is enough grounds to seize a package if an official suspects that commodity is certain illicit type. So writing something on a package is neither a 100% safe although can generally be one of the many factors that lessens chance of scrutiny. If it would be simple as that, there would likely be containers of "baking powder" importe