- Moon: Mom... I think I'm a crescent.
- Earth: It's just a phase, honey.
Hello! This is just speculation but they could have had Mary use any perfume but they chose to invent one that literally translates to 'light of the moon'. We all know John is Sherlock's conductor of light meaning that John is the light of the moon. He is the sun to Sherlock's moon. Mary wearing it suggests that Mary at the moment owns John. But it's a crescent moon, not a full or even half moon. It could suggest that at most, John can never completely be Mary's in the way he's Sherlock's (1/2)