MapServer allows you to define styles for features. These can be stacked on top of each other. Common For full details of the MapServer LAYER>CLASS>STYLE Object please see the MapServer MAP Documentation.
Common simple style settings are:
...
If the symbol that you wish to use is quite large it is advisable to offset it in order for the “PointInfo” search to return the correct results. Normally the symbol will be placed with the top left hand corner at the coordinates of the point. If a user then clicks on the centre of the actual symbol this may not fall within the “PointInfo” tolerance (defined in the webconfig - <add key="MapPixelTolerance" value="10"/>) and incorrect or no results may be returned.
...