The definition of "subtle" -- fine or delicate in meaning or intent; difficult to perceive or understand. Let's use it in a sentence: The guy gawking at Sienna Miller in this photo is not being subtle.
Sienna was walking around London over the weekend, apparently turning at least one head. Miller was spotted here by photogs after visiting a pet shop in the area.
Cameras also caught Sienna out over the weekend with her beau, Jude Law.