Here's why:
* Shape: Alien is famous for its distinctive, smooth, egg- or pebble-like bottle.
* Color: The original and most iconic Alien perfume is a deep, vibrant purple.
* Popularity: Alien is a well-known and widely available perfume, making it a likely candidate if you've seen it before.
If you're still unsure, you can try searching online for "Alien by Thierry Mugler" and look at the images to see if the bottle matches what you remember. There are also other Alien flankers in different shades of purple with similar bottle shapes.
Good luck with your search!