Extra sensitive pores that have developed above the leech's mouth, similar to ones occurring in sharks and catfish.
Many people new to the creatures mistake them for nostrils, but this is not the case! They act as sensory pits, detecting vibrations in the water. On land, they are functionally useless.
Note: These should only be very small dots or squished little lines - longer lines that bear too much resemblance to actual nostrils are not allowed!