Why do you care about the rendering? Does the structure meet the definition of the tag “ruin”? Than tag it as a ruin. It’s not you fault that mapnik or osmarender wont’t represent this faeture with a proper icon. Of corse you could make a proposal to have the renderingprograms (and there are much more than just mapnik or osmarender) drawn ruins into the maps.
I think it would be better to use something like historic=fort, ruins=yes in this case.
I think Osmarender will show this the same as historic=ruins (or historic=anything else), ie just a point with the name. I agree that it would be nice to get some more map symbols for historic things.
I’m happy to add data to the DB, but I also use the DB. I added this fort a while ago, and yesterday was trying to use Maverick on my Android phone to find this fort, which uses pre-cached tiles rendered by mapnik. I was dismayed not to find the icon on the map! I had to find it by remembering mostly where to turn.
I’ll try out the historic tag, and if that fills the bill, great. Otherwise, maybe I’ll suggest a new one.