"Please signify the importance of this event."

[russian80]

How idiomatic would "Please signify the importance of this event" sound if it actually was to mean "Please substantiate in writing the importance of this event" ?

 

[Loob]

I would be very puzzled by your sentence, I'm afraid.

"Signify" doesn't mean "substantiate in writing".

 

[bibliolept]

The alternative phrasing is at best very odd if not downright confusing.

 

[russian80]

From a Russian school olympiad:
https://scontent.fmaa5-1.fna.fbcdn.net/v/t1.0-9/41244230_330701214166313_3638354452429144064_o.jpg

 

[Uncle Jack]

"Signify the importance of such events" means nothing more than "say how important such events are/were".

 

[bibliolept]

"Signify the importance of such events" means nothing more than "say how important such events are/were".

That is being generous! For most, this usage of "signify" would be thoroughly baffling.

 

[Englishmypassion]

How idiomatic would "Please signify the importance of this event" sound if it actually was to mean "Please substantiate in writing the importance of this event" ?

"Signify" meaning "to be an indication of or to give a meaning to something" is not used in the imperative. Things, actions etc signify/indicate or show the importance of something.