People mark coins, because it allows you to track where your dump coins are going.. Allowing you to attempt dumping in places where you won't be receiving them back.. From my experiences and I average about 4 boxes a week, it not worth my time.. I have yet to receive a half back.. Now if you are searching as much as Tim, who does more in a week then I do in two months, then I can see why.. I do think Tim is going a little overboard and bringing too much attention to himself, which might lead him to getting cut off .. If you do mark, you should attempt a simple way that will allow you to monitor , but also not have it noticed by the banks or suppliers..