I have heard it is not listed on Poloniex because it is considered a security which means Poloniex as a US company must register with the SEC.
In other words Polo cannot legally list ICN. Is this true?
No, that is a myth propagated by a known troll trying to crash the price. ICN is listed on Kraken which is also based in the U.S. The reason ICN isn't listed on Poloniex is because the developers do not want it to be.
And it was one of the wisest decision by devs.It helped ICN price stay above ICO price because most of polo trade is speculations.