I agree with lacanau;

Most airport codes are very easy to remember and/or guess. For example:

SEA - Seattle, my hometown, very easy
DEN - Denver
SFO - San Francisco, another cinch
PDX - Portland, see how easy
ORD - Chicago, a cake walk
IAD - Dulles
CVG - Cincinatti

As you can see, ALL airport codes were made to be easy to guess, cause who wants to always be flipping through a code book?