Here's my extension to the classical pigpen (Freemason's) cipher. It is backwards compatible with the old version. I simply add numbers into the diagonal parts of the graphic, which adds 10 extra symbols, coincidentally the same as the numbers we use to count with.
The thing that makes the Pigpen cipher so cool is that it can be easily memorized. One of the biggest draw backs has been that it doesn't include numbers, but this takes care of that.