By default we can't trust anonymous notes no matter what you say in the note.   OSM gives the warning every time we read an anonymous note:

"This note includes comments from anonymous users which should be independently verified."

So we have to correlate your data with some orthogonal source, and that can take effort.  Of course that orthogonal source can have problems too, it may be outdated information.  The way that OSM works is that YOU, the person who saw the signs, make a note in the map when you see it.  You give the license to OSM to use this data, it shows up, and everyone benefits.