Yes more symbols! A uncovered half-track, then one with the 3 American soldiers shooting from it. (a "The Dirty Dozen" reference)

I have seen 1600s maps of Port Royal that show turtle pens that look similar to your pens. If you were to add some big turtles in the water that might work.

A thought, coming in to this late, is to check the flavor text in the Mistborn books by Brandon Sanderson. Which may point to some detail things to through in.

Volcanic dust on roofs, and roads for example.

I posted some new maps, this time Cosmographer. The maps are some of the maps for a Traveller adventure called "Deep Shadows" (which I did not write). The original was written with ascii art. Also the adventure is posted in few places on the internet.