said by OZO:Because I'm afraid, that the clerk, who will use it, doesn't know abut ISO or any standards at all...
So what? No reasonable person would be confused by an ISO date, especially in the US, where month already precedes the date in the numeric notations, and either way, you can't make a mistake which number is the year when you use 4 digit years.
And I would not buy any arguments that banks could possibly afford to hire complete idiots as staff, so, I don't see any problem with using ISO8601 when drawing a free-form cheque in the US. I never had a problem even in a small town local bank in North Carolina.