These are the pictures I got from ebay and internet on North Borneo stamps with 8 cents surcharge on 2 cents. This shows how easy is it to find forged North Borneo stamps and it is important for us to know what's genuine and what's not.
Now, as outlined above, [A] and [B] are genuine and [C] and [D] are forgeries. Just by comparing these pictures, I'm sure you'll get the idea. But anyway, let's start by looking at these pointers:
1. If you compare the perforation between the genuine stamps and the fake stamps, you'll notice that the genuine are perforated 12 while the forged stamps are perforated 14. This is very important as most forgeries on the 2 cents stamps are perforated 14 rather than 12. The height of the stamp is approx. 22mm and by counting the vertical perforation you'll get about 13 perf. or no more than 14, whereas in the forgeries you'll often got 16 or more.
2. If you measure the letters of the surcharge (e.g. the I, E or T) in the genuine stamps you'll get about 2¼ mm high whereas in the forgeries it's only 2mm high. Unfortunately, having the right height does not necessarily mean the stamp is genuine because another batch of forgeries on this stamp have the same surcharge height as the original.
3. Now if you look at the letter "H" in the surcharge and compared it in both stamps, you'll notice that the feet of the H are joined together quite clearly shown in picture [B]. If you now look at the forgeries you'll appreciate that the feet of the H are wide apart. In picture [D], the feet of the H are very close together but they are not joined.
4. Look at the "S" letter now. In genuine stamps, the bottom half is considerably bigger than the top half. In forgeries the "S" letter is perfectly upright and the top half and the bottom halves are about the same.
5. What about the shade? Stamp [C] has a red-brown shade and is known as the Genoa forgery probably by the work of N. Imperato.
There are several other subtle differences, but I think that's all we need to know for now. Pointer no 1 is especially important and should be remembered all the time when looking and judging at this stamp. Comments are always welcomed :)
 Album Weeds: How to Detect Forged Stamps Part V by Earée