Behold, he comes with the clouds, and every eye shall see him, and also those who pierced him, and all the tribes of the earth shall wail because of him.
Then if any man shall say unto you, “Behold, here is the anointed!”, or “There!”, believe it not. For there shall arise false anointed, and false prophets, and shall give great signs and wonders; insomuch that, if it were possible, they shall deceive even the elect.
I believe by simply reading these two texts (although there are many more) it should already be perfectly clear how to tell the true anointed from the false ones.
When Jesus the anointed comes on this Earth for the second time, everyone shall see him and everyone will know. So if anyone has to tell you “Here is the anointed” or if anyone has to explain themselves, or show miracles, or whatever other manner of ‘proof’, no matter how many ‘supernatural’ things they display, how much fire they call from the sky… they are false.
There won’t be any doubt whatsoever who he is when Jesus comes.