The word "since" is a conjunction introducing a coordinating clause in the structures presented by the OP; "since + subject + verb" forms a subordinating clause.
According to grammar, when a subordinating clause with "since" comes before a main clause, you put a comma after the subordinating clause. So the first structure i.e. "since + noun + verb, noun + verb" is correct, whereas the other structure without comma isn't correct. Look at the following sentences in the first pattern:
Since Adam is going, Peter is going, too.
Since you've finished your homework, you may go out and play.