"Signal" or "sign" that shows something

[Rachel Adams]

Hello.

I have a question about word choice. Can I use "signal" and "sign" in my sentence?
1. "Her constant questions about suicide could have been a sign/signal that something was wrong" or perhaps "an indication".

2. "Her constant questions about suicide could have signalled that something was wrong."

3. "Her constant questions about suicide could have signalled to/for something serious that was going on."

 

[Yankee]

Yes. They are both OK, but I don't particularly like "to/for" in 3.

 

[Rachel Adams]

Yes. They are both OK, but I don't particularly like "to/for" in 3.

Is "for" the right preposition?

 

[Tarheel]

I would use that there, thus:

Her constant questions about suicide could have signalled that something was wrong.