Choose a target numeric base:
We start by making a series of 5x7 bitmaps that represent the letters and control codes in your input:
Note that there are five solid characters at the head of the signal, and seven solid characters at the end. This is called the "meter" because it helps set up the rhythm of the 35-bit sections (as well as reinforcing the importance of the prime factors).
The next step is to wrap up the data in a kind of "container". We interleave the characters with five binary zero bits, which separates the meter blocks and calls more attention to the significance of the number 5. An added benefit is that it makes each character unit fit exactly in 40 bits (5 bytes) for easier processing on computers which process data in multiples of 8 bits.
Next we set up some surrounding empty space, called the "silence". This is just a steady stream of 0 bits before the leading meter, and continuous 1 bits after the trailing meter. Without the silence included in the message itself, then two consecutive USCII strings in memory (for instance) would have meter bumping up against each other and obscure the meaning of the meter length. For meaningfulness in that case, we choose 7 "character-sized" 40-bit units of zero silence in the beginning, and 5 40-bit units of one silence in the end.
If the recipients of the message are mathematically-minded, they'll notice that 35 is a semiprime number...and thus only divisible by 5 and 7. This should cue them into the idea of trying to decode it as a 5x7 bitmap. See if your friends with geek-cred can figure it out, or send them the decoder if you are feeling generous. :)
(Thanks for stopping by! If you find ideas like this interesting, then you may also be interested in some of my other projects...like blackhighlighter. It seeks to aid transparency in communication by making it easy to publish most of your correspondence in public, while still committing to what you said in the hidden parts. Check it out!)