A market might be for how many laws he signs. He has signed more than the last 4 presidents in the first 120 days or so.
Also, how many Executive Orders he signs. He's busy on that front as well. And then you could have a followup market: How many of his Executive Orders get held up by some court or other.
It seems uncertain to me how significant is the pure numbers of laws signed. The laws for naming post offices are legendary for being exercises in ineffective legal activism. Similarly, the number of executive orders is less important than their content. Not every order reaches the importance of the Emancipation Proclamation.