Going through the First Edition MM I count:
8 fully exposed female breasts
6 somewhat obscured female breasts
2 depictions of female pubic hair
1 Centaur penis
It seems to me that TSR considered their audience to be primarily adults.
That book would never get published for D&D nowadays.
Wow, showing a horse dong is now adult content?
Note, I said Teen, and YA, not children. That means PG 13 for those in Canada. Which means nudity is ok.
What is not ok are graphic depictions of violence, torture, rape, and all those naughty bits that are very much not Grandma friendly.
The fact that D&D has always glossed over these things leads me to think that the game was always PG-13 at the very outside.
But, I was specifically asking about marketing. So far, I've seen one image that might be considered directed at an adult audience. The rest has been very much teen (and chainmail bikini chick is hitting the teen boys thing pretty hard as well.

)
To be fair, I always thought the art in the 1e Fiend Folio was a fair bit more mature. Arms being ripped off that sort of thing.
Look at the difference with something like Vampire to see what marketing to an adult audience looks like. D&D gets the D&D Saturday morning cartoon and a couple of execrable movies. Vampire gets a prime time night time TV drama and the Underworld series of movies (granted the Underworld movies weren't really by choice

).
What marketing, over the past thirty or so years, has been targetted to adults by TSR or WOTC? Where are the prime time TV ads? What adult magazines - ahem, I don't mean THOSE ones, I mean things like Nature, Popular Science, that sort of thing - show D&D ads?
Heck, it's only been in the past few years that D&D managed to get out of the toy/hobby shop ghetto and into mainstream bookstores.
So, again, at what point in time has the advertising for D&D been targeted at the 25-45 crowd? At the 45+ crowd?