Good morning, I wonder: When can one marry after the death of a parent? Must one wait a year? Does it make a difference if the ketubah is already signed? Thank you,

ב"ה Shalom Shalom, In principle, one may marry after the death of a parent within the year, but after the "Shloshim", the first 30 days of the year of Avelut=mourning. (Shulcha Aruch Yoreh De'ah 392). Depending upon each situation the details may vary. May you enjoy many happy occasions.