Is 'pin-up' considered to refer specifically to glamorous/sexy images?

Solution 1:

It's not a single word, but pullout poster seems to me to avoid the sexual connotations and to convey precisely what kind of poster is in scope.

Solution 2:

Pin-ups do generally refer to sexual images of celebrities and models, often of the nude variety.

I believe the term you are looking for is centerfold.

Note that while a pin-up is a type of centerfold, not all centerfolds are pin-ups (in the sexual sense). I used to subscribe to a nature magazine wherein the centerfold was typically of a wild animal.

Edit: Wikipedia reveals that the term centerfold was coined by Playboy's very own Hugh Hefner, so it's not free of sexual connotations for some. Probably because it sounds like the more neutral of the two terms, though, it's the one that has been picked up and used by publications like Time and National Geographic.

Edit #2: You might just call it an insert or a photographic insert. These have no dangerous associations.

Solution 3:

I'd avoid centrefold, which can be much more explicit than the often retro/50s pinup.

What I'm after is "a cheap, lightweight poster, roughly A3 or A2 in size." (My specific purpose is for a promotional item I think would be nice for Writers.SE.

I agree with Barrie, stick with promotional poster. In fact, the simpler poster definitely fits the bill:

A poster is any piece of printed paper designed to be attached to a wall or vertical surface. Typically posters include both textual and graphic elements, although a poster may be either wholly graphical or wholly text. Posters are designed to be both eye-catching and informative. Posters may be used for many purposes. They are a frequent tool of advertisers (particularly of events, musicians and films), propagandists, protestors and other groups trying to communicate a message. Posters are also used for reproductions of artwork, particularly famous works, and are generally low-cost compared to original artwork. Another type of poster is the educational poster, which may be about a particular subject for educational purposes.

Solution 4:

The OED's definition of pin-up is:

Of a photograph of a person: intended for display on a wall, etc. Of a person: being, or worthy of being, the subject of such a picture; glamorous, attractive.

I think we'd need to know a little more about the poster you have in mind before suggesting how it could be described.