Perseus utilizes a hidden character and interpretation puzzle to complete the partial URL on the bottom of the card.

If you examine the card closely, you’ll notice that Perseus’ shield has a series of greek characters that alternate with the missing characters in the URL puzzle code.

Sigma = Σ Omega = Ω Delta = Δ Phi = Φ

When you convert these characters to their English spelling equivalent and combine them with the partial URL on the bottom of the card you would find the following URL:

5sigma5omega5delta3phi3psi.com

When visiting this URL, you are presented with an audio recording of Charlie Neil. After downloading this file and examining the meta-data, you will find the puzzle completion link.