I am absolutely no friend of onscreen messages and as long as Google hasn't finished its new eyewear, this isn't logical at all. My suggestion is to remove them if they aren't necessary or to turn them into something physical.

For example, the broken door could just rais a bit, then there are sparks, and it closes again. That makes the player automatically think: "Oh, it's broken!"

Don't describe situations with words, describe them intuitive with visuals

"That doesn't seem to work" is a lock to which no key works FWIW
You get it when you use Door_LockedRaise with an unknown locknumber.

Agreed. Onscreen messages like this seem a bit amateur, though the locked door are an exception to this IMO.

For the locked doors, they can be made to buzz if you do not have the key alongside the message, like in Quake/2?

Yeah, just need an SNDINFO entry.. and of course the proper sound effect.

The Nuclear Sandwich message was intended as a subtle "replace this!"" -- it's pretty obvious and a n objective update will follow anyhow, in place of the message.

This can probably be closed, since the "That doesn't seem to work" [s]is dismissable[/s] has its own thread already.