If I am auditing for compliance of Reg.CC at my bank, how can I determine by reviewing the deposit slip which contains the fractional aba number, the local versus non-local checks for non-"on us" checks?
thanks, I am new and you guys know everything!

I'm not sure if your the dame Anon I responded to earlier but try this Routing number definitions
You may also try the Federal Reserve Website and this article of changes to check processing regions

Actually, I don't think that is the best way to do it. I think you would need to go to the film of the deposit to do it accurately. If you just look at the fractional number, how can you determine if it should be a next day item, i.e., cashier's check?

For the reason rlcarey mentions, many banks attach copies of the checks to their copy of the hold notice solely to facilitate third party reviews. The regulation does not require it. However, as you have discovered, the number does not tell you everything you need to know. In addition to cashiers checks, the number in the MICR line doesn't indicate state and local government checks or payable thru checks. You do need the list of "local" numbers, it's just not enough to answer all your questions.

what are they?

Most checks are still printed with a set of numbers that look like a fraction. They may look like 53-574/113 or
53-574
113

These are throwbacks to the days when checks were sorted mechanically by machine operators. The top of the "fraction" has two parts. The first number (53 in the example) represents the city or state the bank is located in. Numbers 1-50 were for the 50 largest cities in the US in the early 1900s. Numbers 51-101 are states and territories. The second part of the "numerator" (574) is a unique number from 1 - 9999 assigned to the bank.

The bottom of the fraction (113) indicates the Federal Reserve District (1 in this case) and other routing information.

It used to be the "standard" that the fractional symbol -- or at least the top of the fraction -- would be written next to the check amount on deposit tickets to identify the bank on which the check was drawn.

With the advent of automation and the use of the MICR line at the bottom of checks to route them for payment, the fractional symbol is really of vestigial value. And with decentralized processing and interstate branching, assigning a bank to a state is often useless.