[It is a tradition. Maybe not an old earth tradition, but their tradition. And considering she's already had a few kisses today it should probably be on her mind, but when she sees Reid there is a more important thought on her mind.]
Hey! [She actually lights up a little and gets up from her seat to kiss his cheek completely unprompted by robot intervention.] Thank you. That was really sweet.
[If it helps any she actually has a gift basket sitting on the seat next to her.]