Girls, Giggles and Garters
This is a magazine for the discerning male connoisseur. It is unclear who publishes it nor who has a financial interest, but it is possible that the Seamstresses' Guild takes a close interest in a print publication that would somewhat overlap its own specialist services. (Or perhaps the Guild of Ectysiasts, Nautchers, Cancanieres and Exponents of Exotic Dance considers this to be their professional area of expertise, and one of those demarcation disputes could be going on)
We learn of its existence in Thud!, where Nobby Nobbs' one-time girlfriend Tawneee is revealed to have been not only Miss May, but also part of Miss June, because even the centrefold wasn't wide enough - that's the only way they could fit her all in.
As Tawnee's day job - well, evening job, anyway - is as an exotic dancer, then we can discern that the raison d'etre of G,G & G is the reproduction of artistic shots of ladies wearing very little clothing. With iconographs freely available, and once the Ankh-Morpork Times' technical staff had solved the problem of how to get colour reproduction in mass-market publications, a development like this was bound to happen... (On Roundworld, the first photograph ever taken was a village street in France. Hard on its heels was the second photo ever taken... and yes, this involved a naked lady, some strategically positioned urns, and a small length of gauze. After careful research, we can, however, categorically discount the much-rumoured presence of a Shetland pony.)
Annotation
On Roundworld, specifically in Britain (a nation that has never got the hang of its collective attitude to sex) there actually were magazines of the general Girls, Giggles and Garters genre, that featured fairly innocuous cheesecake shots of young ladies in their underwear or in bathing costumes, often posing in nighties with favorite teddy bears clutched protectively to themselves, or on the beach playing catch with beach balls. This was at a time (1953) when America was being treated to the first issues of Playboy, and as for what was coming out of Denmark...
G,G, & G is also alluded to in Good Omens, as part of Aziraphale's mind-set concerning what is chic, fashionable and cutting-edge modern, which in the opinion of Anthony Crowley, grounded in about 1952, and resolutely stayed there. There is also an allusion that when she was younger and had more to offer, Madame Tracy was a model for G,G, & G - her bedroom is not that of a typical dominatrix, as it has several shelves' worth of period cuddly toys.
It is entirely possible that both Aziraphale and Crowley had a hand in creating this magazine. Maybe it was part of their Agreement: so that Aziraphale could report back to the Metatron that he had thwarted a Satanic plot to ensnare British men into the sin of lust by making the magazine so tame that nobody in his right mind would feel any lust. (ie, such soft-core porn that it was practically invertebrate). Crowley, on the other hand, could assure Beelzebub that soft-core porn mags fitted in perfectly with his plan to spread the maximum amount of sin around the maximum number of people. Imagine several hundred thousand men, in a moment of Sloth and idleness in such as which the Devil will surely find them interesting things to do, not only getting tainted with the Sin of Lust on seeing the front cover, but, on opening the pages, realising there's nothing much there to lust over, feeling frustrated, and slipping into the Sin of Anger - three deadly sins for the price of one! (And if Crowley has taken good care to spread the information, you might add the Sin of Envy: already dissatisfied with the product available, the British consumer of such a mag might feel jealous of what the Americans and the Danes - especially the Danes - are allowed to see that he can't...)
Girls, Giggles and Garters is also mentioned in Only You Can Save Mankind. Johnny Maxwell is looking pale and ill, because he has been up for something like five nights with very little real sleep. (There is a reason for that - saving the Scree-Wee). Not knowing this, Johnny's grandfather blames it on Johnny spending too long in front of that dratted computer. Why can't he do what we did in my day - get hold of a copy of Girls, Giggles and Garters, it'd be far better for his health and complexion... there's got to be something wrong with boys these days if they spurn honest girlie magazines for computers!
The British glamour mags of the 1950's had names like Spick and Span, Pin-up Pix, Glamour Figure Pin-Up, and the wonderfully named Blighty. They're all out there on the net somewhere if this sort of thing interests you... for genuine artistic and academic study, naturally...