There's no Form 186 B
There is no ECFMG Form called 186 B!
There is what's called Part B of Form 186.
Part B, is the part that has to be signed by your medical school official.
Part A, is the part that has to be signed by notary public.
Form 186, will be presented to you when you finish the online part of the ECFMG application. You have to print it, sign it in front of notary public and then send it to your medical college for signing and then your medical college should send it back to the ECFMG.
PS- If you are presented with something called Form 186 B, please let us know about it because this is the first time we hear of such thing.