There are a combination of letters on a table that sits at the front of First Presbyterian in Golden that look like this:
Iota Eta Sigma
I puzzled over it for a while and finally asked Earl Palmer from University Presbyterian in Seattle.

One of the things I like about talking with Earl is that he just doesn’t give you the answer. For instance, Earl could have just said, “It means Iota Eta Sigma.” But no. He explained that it’s one of the Greek words for Jesus, coming from the Greek word Ιησους (Iesous) which translates to ‘Jesus’, but is often just shortened to Ιησ. To get from Ιησ to IHS, make the former all upper case letters: ΙΗΣ. Almost there, the last thing you need to know is that Σ is the letter Sigma. So, take the ‘S’ from Sigma and you have IHS.

Earl then went on to explain Χριστο (Christos) that means Christ (natch) and is often abbreviated to Χρ.

And finally, ΑΩ (Alpha/Omega) which refers to Revelation 22:13:
From www.biblegateway.com:

I am the Alpha and the Omega, the Beginning and the End, the First and the Last.

Here’s the site I used to lookup the exact Greek definitions/spellings of what Earl gave me: http://www.htmlbible.com/sacrednamebiblecom/kjvstrongs/STRINDEX.htm

Wikipedia also has an article on the Christogram.