on a serious note

[paris 06]

I am not sure if the underlined is replaceable with " on a serious note" and what exactly does "note" mean?

- People tend to be on a serious side today


Thank you in advance.

 

[5jj]

I am not sure if the underlined is replaceable with " on a serious note" and what exactly does "note" mean?

- People tend to be on a serious side today

Your sentence sounds strange to me. It would sound less unnatural to me as: people are (rather/a bit/a little) on the serious side today.

The expression with note is used when a speaker wishes to turn a conversation/discussion which has been fairly light in tone in a more serious direction.

A: Our works canteen is going to be run by a catering company from Hamburg.
B: Oh, so we'll be getting hamburgers for lunch every day.
A: I hope not! On a more serious note, the canteen has been heavily subsidised in recent years, and we need to consider whether we can afford to carry on like this.