[LifeTech]

This is very aparrent on many Toyotas including my Highlander.

Toyota Sprays a liquid WAX anti rust protectant that lines all the doors. When it rains the dirt along with the Factory applied wax dripps out of the drain holes. Yu will find this drip running down from all the door drains as well as the door handles.
It tends to be more noticeable on lighter colored vehicles. But is will come off with any good cleaner wax or light compound.

It usually wears off and stops dripping after a couple of seasons of hot and cold climates.