Common/Traditional:
* A tissue or napkin: A classic way to blot lipstick.
* A coffee cup or glass: Leaving a trace of her presence.
* Her own fingers: When applying or fixing her lipstick.
* A man's cheek or collar: A romantic gesture, or perhaps a playful one.
* A mirror: After applying her makeup.
* A cigarette: A vintage image.
More Personal/Symbolic:
* A love letter: Sealing it with a kiss.
* A photograph: Adding a playful or flirtatious touch.
* A pillow: Signifying intimacy or a good night kiss.
* A goodbye note: Leaving a lingering reminder.
* A journal or diary: A personal and intimate trace of her.
Creative/Unexpected:
* A piece of art: An unconventional way to make a statement.
* A car window: A playful or teasing message.
* A public wall (vandalism): Perhaps a form of protest or rebellion (though not condoned!).
* A fortune cookie: A unique and personalized message.
* An evidence bag: Making the lipstick mark on the bad guy.
The best answer depends on the context you have in mind!