Help identify these protrusions on my leaky roof
I am not quite sure what that copper/brown colored thing is but the two round things look like the covers off of one gallon sized cans. My guess is that some previous owner was patching up a leak in that spot and there were a couple of holes in the roof.  They were using patch cement similar to what you are setting out to use and decided to stick down these can lids over the holes. Quite possibly the can lids came from their patch cement cans themselves. 

If you can tell us a bit more about that copper colored thing it may be possible to clear up what that is as well. Maybe it was something placed on the lid to help hold it in place.