Romantic kissing or other interaction can represent:
Emotional intimacy (emotional trust and openness), interaction, or a feeling of closeness with someone
A replay of when you felt close to someone
Liking the person or wanting to know them better—and not necessarily romantically!
If it is unwelcome, it can represent an intention or attempt at emotional intimacy that you consider unwelcome from someone else (such as a stranger telling you their secrets) or a feeling that someone is trying to act too familiar (such as acting like they are your close friend when they aren't).