If this forum is considered a public place, and you advertise the sale of shares of a security (which only needs to pass the Howey test to qualify), then you are under the SEC jurisdiction in the US.
wouldn't that only apply if you are in the US?
Maybe. IANAL, but if you are in the U.S. and advertise to other people in the U.S. then its SEC jurisdiction. Even if the website is across the globe.
If you are not in the U.S. and advertise to people in the U.S., then it will come down to the local country willingness to cooperate with the SEC. I think the FSA is more than willing to play ball in an investigation for instance. (U.K.).
If you are not in the U.S. and you advertise only to people not in the U.S., the the SEC has absolutely no jurisdiction to do anything to you. Some other authority might though.
At least this is my understanding.