Ok so here's another one:

D(c)ash... - 'c' is silent
D{c}ash
D[c]ash



Then there's a marketing campaign:

We have a bunch of people each representing a certain group in a society: teenagers, collage kids, young profesionals, working class, middle class, seniors etc...
So everyone buys something that's not illegal but wouldn't want to parade about that and keep it on a hush hush..
And at the end of a short video clip we have each protagonist putting a finger to his mouth in a sshhhh. fashion

An the final curtain:

   D[c]ash - [c] is silent...
      [c] - cryptography
      [c] - cash
      [c] - caution (maybe not)
      [c] - ....

Of course it has to be done with fancy graphics and animation