Yes,it is also correct.
Kan man sige "du skriver under" i stedet?
Is there a separate way to say to underwrite "eg. In insurance" in Danish?
You sign. Just bald like this, could be an imperative. As this is a lesson about the imperative, how can DL mark it wrong if I put "du underskriv"...?
In that case, there has to be an exclamation mark at the end.