On a related security issue many of us face these days, here's a suggestion for those hard to remember PIN numbers.
If you've got several cards in your wallet/purse/pocket or wherever, and you probably favour 1 or 2 of them most of the time, how do you remember those infrequently used ones (assuming you haven't done something silly like use the same PIN on all of them) ?
I carry a credit size laminated card containing a matrix and my PINs are hidden on it. All I have to do is remember which card is which line, column etc and the secret is then that it's the 4 digits after the Key.
Here's an example I made up this morning; not my real one!

- matrix.JPG (38.79 KiB) Viewed 3129 times
So the 'Key' is the 1st time a specific number appears on a line.
So using the example I've made up above, if 8 is the Key, then the PIN on the 1st Line is 7910, the 2nd Line is 6611, the 3rd line is a dummy for extra security and the 4th line is 2660.
You can make up any rules you like, because it's your own security system. Have vertical numbers or diagonal ones if you wish, even a square block. You could even have 4 numbers on a line, but then the PIN is actually Plus 1 to those 4 numbers; the options are fairly high and unique to yourself.
You can even use it to record other combinations, such as padlocks, or that key case that's on the elderly relatives front door for emergency access.