Before we get into the specifics of symbols (which, in the case of this poem, shouldn't be a particularly difficult explanation), I'd like to touch on the meter and rhyme scheme. If you are familiar with the concepts of meter, you may have noticed that this poem is set to what would seem to be an altered iambic trimeter. The alteration is very slight: a substitution of a single tribrach in place of the last iambic metra of every odd line.