ArcGIS always places a little symbol, called a patch, next to the text name for your layer. Did you know you can override the default to access a greater variety of legend patches that better communicates what your layer is?
In Legend Properties, make sure you are on the Items tab. Then just double click your layer to bring up the Legend Item Properties, and head to the General tab. Finally, check the box that says Override Default Patch, and select the patch of your choosing.
Voilà! You have a new patch to better reflect your dataset.