The absence of structure , color , nectaries , smell point towards self pollination.
Cross pollinated flowers produce brilliantly coloured/scented flowers to attract insects that transfer pollens from one plant to another. Cross pollinated flowers that use air as agent produce huge quantity of pollens.
We can also differentiate according to the reproductive organs present in the flower. For example, if a flower contains only androceium or only gynoceium it performs cross pollination and if a flower contains both androceium and gynoceium it performs self pollination.