How to override the Is operator?

I have a bunch of objects scattered in a database. All of them have a numeric ID and I want to override the Is operator so I could do this

if objA is objB then ...

currently it compares the memory location i think or whatever .net does to keep track of class instances. I want to override it so it would compare the ID's in the objects instead.

Google is of no help since "Is" is filtered out I think.