More than likely the C1 58 is some type of unit or "rack" number. For example it could represent Company C, 1st Regiment, soldier number 58. Since these sabers did not have serial numbers, such markings were a way to deter theft and make the soldier responsible for his equipment.

Unfortunately, without additional information the question arises of which 1st Regiment? 1st NY, 1st PA, 1st MASS, 1st MAINE, etc.

While one would guess that it is a Civil War unit, these sabers continued to be used during the Indian War period, by militia units, etc.

John Gross