Definition of Mass in Multiple Mass Oscillators

In an exam on seismics and earthquake proof design I had a couple of days ago, there was a question on multiple mass oscillators in the form of a simply supported beam of length $$L$$, stiffness $$EI$$ and two point masses $$M$$ at the points $$x_1=\frac{1}{3}L$$ and $$x_2=\frac{2}{3}L$$.

Although I know, how to solve such a system, I was a bit confused about the unit of measurement of the mass. Both "masses" featured a value of $$M=1'000$$ $$kg\cdot s^2/m$$. At first I thought it was a typo meant to be $$[kg\cdot m/s^2]$$, which I would have interpreted as $$M$$ representing a force, i.e. $$M=m\cdot g$$.

However this denotation appeared over and over again on this exam (and of recent years as well).

A classmate assumed, you had to multiply this "mass" $$M$$ with the readings from an accelerometer. This would make sense to me in regards to the units but not as a logical principle.

Why would you denote the mass-property of an object neither by its mass, nor by its weight? Is anyone around here familiar with such a concept either in seismics or any other field?