As a couple who has actually put a pineapple in their cart upside down, we have never even gotten an acknowledging reaction. We're just not sure how many people (whether in the lifestyle or a vanilla) know what it means.
It seems to us that if you are out in public and want to discreetly "send a signal" to other swingers, then wearing an SLS hat (or any article of clothing with the SLS or other swinger web site logo) is the way to go. Vanillas will likely not recognize the logo, but swingers certainly will. You can pretty much make up something believable as to what SLS stands for should a curious vanilla ask you about it.

