I found something on the Internet (at http://www.interment.net/data/us/ca/losangeles/longbeach_mun...), which you also may have seen.
It explains the name "Signal Hill". At the bottom of the page there is a listing of "all existing and legible headstones and markers" in that cemetery, and, unfortunately, I don't see the surname Carroll listed.
I just wanted to bring this to your attention. Best of luck to you.