Please, please, please , please no...
Just kidding. Doesn't thrill me (translation I'm not interested in being an officer), but it seems a reasonable category and I would probably post more than the "one to get the icon".
Sounds like you already have it pretty well defined - my first concern was the transient nature of signs, but you seem to have that covered. Off the top of my head it seems like it has a good prevalence, Maybe a little on the high side, but nothing like benchmarks or national register of historical places - at least not in my area.