I don't think anyone really believes you can stay "anonymous" if you send in a tip anymore with all of the ways to track a person, and maybe it isn't possible. I have been trying to think of a way to get info to the Spierers or LE, if someone at least wanted to tell them where Lauren could be found, without anyone knowing where the tip came from...how could it be done?
Cameras at post offices and many other places...I guess you could drop an envelope in a public mailbox someplace, making sure to use gloves and not licking the envelope, getting the kind with the peel-off strip. If LE did not have your DNA, and your prints are not on file, you might be able to get away with it, even if you leave some skin cells.