Steve McQueen is considered by many to be the "King of Cool" and it is clear that one of the reasons the vintage Heuer Monaco is valued so highly is due to the link with McQueen and the film Le Mans.
How did this come about? Well Jack Heuer was visionary in realising that product placement in feature films and within motor racing was a very effective and economical way of advertising. Heuer already had close ties to event timing and PR from the Olympics but this was to reach new levels during the 1970s, especially in motorsport and F1 in particular.
For the film Le Mans Jack Heuer used his relationship with a Hollywood film set "prop master" to send a box full of Heuer related items (watches, timekeeping boards, stopwatches, patches and stickers) to be used by the actors and on the set as props. It was McQueen who selected and ended up wearing the Monaco during filming (the Monaco appealed to design concious individuals) which is why we now have the McQueen Monaco and not the McQueen Carrera! In fact, McQueen even wore an identical racing suit to his friend Jo Siffert (who has also close links to Heuer through his white "Siffert" Autavia) the famous Swiss Grand Prix driver. Much of the set, including the suit, was adorned with the Heuer logo adding yet more branding to the film at a time when the Heuer Monaco was in its first months on the market.
As an interesting side note to this, one of several vintage Heuer Monacos from the Le Mans film set recently sold in June 2009 for $87000 via Antiquorum. It was worn (albeit only for the duration of the film) by McQueen himself...