A single frame.

A film runs two hours and the tattoo is one frame, so choosing which frame is most of the design. An object or a silhouette usually beats the lead's face — a sign, a car, a hand; a face is a portrait and arrives with its own demands. Film grain and low-key lighting sit well with soft grey. And the final test is simple: someone who has seen the film has to recognise it without being told what it is.