Although AAA which we use doesn't ask us to sign a blank CC receipt for potential dammage to the car we rent, several rental Cos in SXM do it.
I suggest you set-up automatic alerts with your CC company triggering a txt message or email each time your card is charged more than $xxx, in my case, $1. That way, I know immediately if someone charges my CC and I can react without any delay.
In addition, as other posters mentioned, take some phone pictures of the car when you pick it up and when you drop it off.
Better be safe than sorry.