What reference set is the part using in the assembly? Is it using the enitre part reference or a model reference set? Right click on the component in the assembly and set the reference set to model. Also check the reference set in your part to make sure they are set correctly. Format Reference sets.
Those are datums (a datum co-ordinate system), which is a feature in the part navigator.
The best thing to do would be to change the displayed reference set for your component (by right clicking in the assembly navigator) to SOLID, which should only contain solids. That way, the datum co-ordinate system is never brought from your component into the assembly.