A few simple gutter themes for SublimeLinter. I wanted the simplicity of a circle/dot, but found the default size too big/distracting so I created a smaller circle/dot (filled and outlined), and also a simple line (either horizontal and vertical).
Dot (Filled), Dot (Lined), Line (Horizontal), and Line (Vertical)
Copy the Dot and Line folders to your .../Sublime Text 3/Packages/SublimeLinter/gutter-themes folder and restart Sublime Text.