Transaction

j"1NF7i6ZoMDXaJ2Q5M9QFriH74ya6r6vP8uBMiner ID is a keypair that miners use to sign the blocks they mineM±
Miners can put any random data in their coinbase transaction when they mine a block. At the moment, they put their name in there but there is no security. Any miner can put anything there so they can pretend to be someone else for example. It is optional but very helpful for miners to advertise information (miner parameters, fees, etc.) and opens the door for them to be able to offer better and safer services to users/merchants.