Can someone explain "map" in the context of this email? Email link

So the handkerchief has a map on it and map=semen according to this thread. That sounds like he left a handkerchief with dried semen on it just lying around. Except the handkerchief is described only by its color so how would you know it had a "map" on it by that description alone? And even if white=semen why would anyone nonchalantly send an email like "hey I found a handkerchief covered in jizz, want it back? I'll mail it" Am I misunderstanding the email or does map mean something else in this context?