Michael Card's observations cuts to the chase, while the online entry in the Catholic Encyclopedia gives a succinct overview. *If you're interested in a detailed analysis of the symbol, check out Charles A.
Archaeologists found about 70 examples of these kinds of messages in one cemetery alone.
But where did Christians get the idea to use an anchor in the first place?
The anchor appeared as the royal emblem of Seleucus the First, king of the Seleucid dynasty established after Alexander the Great's campaigns.
Big Bang theorists have spent decades looking for antimatter regions of the universe with leading astronomers culminating a significant project by writing in The Astrophysical Journal: "we conclude that a matter-antimatter symmetric universe is empirically excluded." The journal reports a physicist's assessment: "The work is extremely compelling and gives me fresh pessimism" that is, on the difficulty of explaining why the universe even exists.
For a creationist and a secular explanation of this problem, see creation.com's report on the Discovery Channel's How the Universe Works, and see this Fermilab antimatter video: Yet even secular science authorities have begun objecting to the systematic misattribution, and hence, post-dating, of the the claim of expansion.