See, the problem is no guy is likely to just hit on my wife in front of me, or virtually none. And the type that would do so is invariably not going to be the type my wife would be attracted to. And going up to strangers and telling them my wife is available is not going to fly with her either. This is why I was asking if there's some more subtle way to communicate that we're open to it.
The advice I often see is to have your wife go Girls Gone Wild crazy on the dance floor and wear clothes that have her tits and ass hanging out, etc. This is just not her personality or idea of fun. And I'm sure there are plenty of guys who aren't into that type of spectacle either.
Part of the fun for so many is the innocence of the wife, which is lost when she goes dancing on tables and rubbing up on a train of random guys. Not that I might not like to see that eventually too, but baby steps.
I guess the queen of spades image is the closest thing, but it's too common of knowledge for her to feel comfortable with it. She'll be afraid of bumping into a friend and being mortified.