Which of these features are you most likely to find in a modernist poem?
plain statements of the author's personal judgment
accurate statements of abstract philosophical concepts
precise images constructed with as few words as possible
emphasis on narrative sequence rather than language
a definite viewpoint on a controversial topic stated in formal language

If my memory serves me well, the features which you most likely can  find in a modernist poem are being revealed by the third option from the scale represented above : precise images constructed with as few words as possible. This is the main point which can help you to distinguish modernist poem, to be more exact the idea of symbolism which means the less words - the more sense.
Do hope you will find it helpful!