The sonic lipstick was a device similar to the sonic screwdriver owned by the Doctor, and regularly employed by Sarah Jane Smith. It resembled a genuine 21st century lipstick closely enough not to seem suspicious.
“The story of Doctor Who is always the story of the companion, it’s always their story. It was Rose Tyler’s story, it’s Amy Pond’s story – the story of the time they knew the Doctor and how that began; how it developed and how it ended. It is their story. The Doctor’s the hero, but they’re the main character.”—Steven Moffat on Doctor Who