Ok, after a few years, it's time for an update as there are a couple new generations of pretty convincing redials out there.
Here's a common one:
Notice the frames/surrounds on the triangular markers...they are in the style of the white Ranchero dial, but are NOT CORRECT for the black dial. Also, notice how the "9" has uneven thickness in it's curves on top and bottom. Also, notice the subtle serifs on the "3":
OK, here's another one:
Here you can see that the numbers have thicker more modern font. Also, the Ranchero script is wrong and the Omega symbol is thick and fuzzy.
And finally, here's another common one:
Note here that the triangle at the bottom of the subdial is cut short. that is a very easy giveaway that should automatically set off alarms for you. Also, notice how all of the arrows are far from touch the rehout...that's another sign of a redial, however, it could sometimes be due to the watch being fitted with the wrong crystal and tension ring.
and last one. this one was otherwise, very convincing:
But look carfully at the subdial: it should NEVER have concentric rings on the Ranchero:
Also, the arrow markers are just a bit too sharp and exact.
I hope this helps!