For prototypes you should put: "Signs it's a real prototype:". Because now, according to the structure of your post, you indicate that a prototype is a fake in case is has a larger board...
Signs it's a real prototype:
- Bigger boards (regular sized boards can still be prototypes)
- Eprom's / Re-wiring
- Handwritten labels
- Handwritten name on carts
- Standard labels used by company's for prototypes
- Age of the label ===> old labels mostly have a faded look
- Printing on the label ==> old school printing
- Windows cut out for the EPROM's so they can stick out (because they use a chip holder to easily remove and insert the reprogammable EPROM's, the board won't fit in the cart anymore. So they cut windows in the cart)
A good way to learn people how to spot if it's a prototype (or to spot fake seals) is to make a picture catalogue with pictures of multiple prototypes having one or more of the things I mentioned above.
For example, here you can see that my Captain skyhawk prototype and the "A boy and his blob" prototype from nesplayer.com have the same kind of label style.
If you look at the boards however: my prototype has a regular sized board. But it does has rewiring and uses a Eprom.