Well, aside from jokes, if you're really looking for a useful memory rule, there is one that I always use for remembering big numbers.

You need to break down your number into parts from 3-4 digits and remember them visually using projection on your cell phone keyboard. It's easier to show on a picture:

As you can see, from now on you just have to remember 3 shapes, 2 of them looks like a Tetris L and one looks like a tick. Which is definitely much easier than memorizing a 10-digit number.

When you need to recall the number just recall the shapes, imagine/look on a phone keyboard and project the shapes on it. Perhaps initially you'll have to look at the keyboard but after just a bit of practice, you'll remember that numbers are going from top-left to bottom-right so you will be able to simply imagine it in your head.

Just make sure you remember the direction of shapes and the number of digits in each shape (for instance, in 2147483647 example we have a 4-digit Tetris L and a 3-digit L).

You can use this technique to easily remember any important numbers (for instance, I remembered my 16-digit credit card number etc.).