I have seen some old prints where the printer had seem to have written directly on the print before development, to mark an event, and the the writing was bright white. My grandfather has one of a naval ship with this informal, non-stenciled writing on it prominently right below the middle of print, under the main subject. Maybe a dip of a quill pen in fixer, and a quick scribble before it was put into the developer? or some other vehicle like petroleum jelly that blocks developer reaching the surface?