Everyone likes a good mystery, which helps explain why people gravitate towards puzzle ads. They're especially fun to solve, especially those targeting a niche audience, guaranteeing that the average person remains unaware of the brainteaser's agenda.

Remember this un-branded Google ad from 2006? My eyes gloss over just looking at it.

And who can forget poor Ralphie from "A Christmas Story"?  He receives his Orphan Annie Secret Society decoder in the mail and eagerly works on cracking a secret message. Sadly for him, the message was an ad: "Be sure to drink your Ovaltine."

The University of Phoenix launched a print and online campaign targeting military students using code: Morse code.

Ads created by Pereira & O'Dell ran in Military Times AF, Military Times Army, Military Times Marines, Military Times Navy, Edge Magazine and GI Jobs, among others. Carat handled the media buy.

Copy was written in Morse code, save for the University of Phoenix name, phone number and Web address where ads could be decoded.

According to James Brown, creative director at Pereira & O'Dell, "the phone number rings through to military-specific enrollment advisors who were coached on the campaign."

The microsite offers a flattering picture to visitors before decoding print ads. "Welcome. You're here, so obviously, you're inquisitive, persistent and action-oriented. And that's exactly the kind of person that makes a good student. Find out how higher education can help translate your talents into the bigger picture."

Online, soldiers can also send personalized messages in Morse code to their friends, aside from finding out additional information about University of Phoenix programs tailored to military students.

"You see things most students don't. That's what makes teaching you so thrilling," reads one translated ad, seen here. See additional ads here and here.

"The strategy of the campaign is to say 'We get you,'" said Brown. "We know what the military is looking for, what service and support they need, and how people with military experience can help explain to prospective students how this kind of education can fit into their lives. The idea for using Morse code came out of thinking about how to talk to this audience in a way only they would get," continued Brown.