What exactly should SPG address? You were in a property located in a country where that type of behavior is not only completely acceptable but also quite normal. The same be the case for several countries not only in Europe but elsewhere around the world. Should SPG, whether it is an American corporation or not, prohibit locally acceptable practice to confirm to American sensibilities? I'm not sure SPG would last very long in any market doing that nor would SPG be expected to do that.

Have you ever been to a public park in some countries during the summer? Say, Berlin and the Tiergarten? If so, you'll quiet readily know that:

a) there are men, women, adults and children in all states of undress
b) there are absolutely no signs whatsoever "warning" the public that they are likely to see nearly and/or fully naked people enjoying themselves in the sun at all times of day at a well-visited public park.

If you've been to some beach or spa resorts, you'll also encounter nude or nearly nude people. I don't really understand what type of follow-up you think is appropriate. Are you merely trying to invent an issue/objection to receive some form of compensation?