Interesting that someone above mentioned NASDAQ for opening indications. Sorry to say that there are not any opening indications there because there is no "opening" ....and, if you think about it, how could there be? There is no "there" there (no single marketplace).
Regarding listed securities...the opening indications are transmitted to the Regional Exchanges when the opening price is going to be more than a few cents away from the previous day's close (I think about 35cents). RediPlus, of course, broadcasts all this information to the traders.