Write Four Digits for More Protection
Even when you fill them out with a wash-proof pen, your outbound checks may offer identity thieves another bit of primo booty: your complete account numbers for credit cards, mortgages or other loans, which are routinely written (at the payee's insistence) on signed checks.

How to Protect Yourself
Rather than obediently scribbling your entire account number on signed checks—often on the Memo or For line—list only certain digits, such as the last four numbers of your credit card account. Or write down no integers at all. Firms routinely ask you to note your entire account number, but there is no need to comply.