private void checkModifiable() {
		if (!(markers instanceof ModifiableAddressSetCollection)) {
			throw new IllegalStateException("Attempted to modify a read-only marker set.");
		}
	}
Returns the Navigator Icon for this marker set

@return the Navigator Icon for this marker set
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/marker/MarkerSetImpl.java