Throughout the HP series we keep being told that "Harry potter has Lily's eyes".
Which is (implied to be) significant because:
Snape was in love with Lily, and thus it meant Snape had a reason to care for Harry.
Given that we are provided almost no details on Lily and Snape's past it's hard to draw any further conclusion from this, but to satisfy/disprove a personal (and thus subjective) theory of mine: Does Snape have a son?