The user has installed one of the many graphics mods available in teh Creation and Customisation (C&C) forum. You can get various sets of little "badges" like those to make it easier to identify strategic and luxury resources, and some come with little "blips" to see how much food or shield or gold bonus is provided by each one.
There are also some modified little faces for your city screens and F1 display that make it easier to distinguish and count happy, content and sad people. These let you spot cities about to riot, or see the happiness effect of adjusting the money sliders more clearly.
And you can also find complete terrain mods that change the appearance of your world. This user has installed one of these as well, so the forests are the big green splodges, the mountains are rocky outcrops, and the sea is darker than normal.
There are modified cultural borders, units, leader-heads, advisers, user interface dialogs, adviser screens, tech trees .... if you can see it on screen then it's probably been modifed by someone. Browse the C&C forum to see if you like any of them.
All of the mods contain modified versions of existing graphics files in your standard Civ3/Art/ folder. You can install them by moving the existing files or folders of the same name into a safe place, and replacing them with the mod files. The same procedure works for version 1.29f on Windows. I think the Windows expansion packs (PtW and Conquests) also allow you to put the mods into "scenario" folders to avoid having to back up your original ones.