Credentials are all about signaling. But what is it exactly credentials communicate? Is it, "person X learned about topic Y"? I'd argue it's a lot more than that. If you have a degree from Stanford, then the information "this is a person who was admitted to Stanford" has a lot of value in addition to just "this is a person who took Stanford classes". (How much would you care if someone told you they'd sat in on Stanford classes without enrolling? Not very much, right?)
There was an Econtalk episode on this:
http://www.econtalk.org/archives/2014/04/bryan_caplan_on.htm...
I think MOOCs are not particularly good as credentials in their own, but the projects you do in them can be very useful in getting a job. (This is kind of the "human capital" model discussed in the podcast.) Maybe their lack of exclusivity is part of the reason they're not more positive signals on their own.
Think about the projects you'll do and what you'll be able to say you did after the course is done.
Don't count on the credential itself to say too much.