Hi Scott,
The symbol 'IC' means that outport is getting its initial conditions from the block connected to it when the 'Source of Initial Output Value' of outport block is set to 'Input Signal' or if it is set to 'Dialog' with empty matrix '[]'.
Refer the following example for more information regarding this:
This is the effect of the 'Underspecified Initialization Detection' option being set to 'Simplified' in the Configuration Parameters. (Refer the following link for more information regarding this: http://www.mathworks.com/help/simulink/ug/simplified-initialization.html)
Hope this helps!
Gautam
