Go pick up a scope from radio shack for like 12 bucks. Cut some leaf matter and look at the trichomes. If they are clear it's not ready. If they are cloudy you can pull them. If they are amber it's totally ready. Many people suggest (myself included) you pull them when the trichomes are a mix of cloudy and amber.
I know you want an answer but you just cant tell by looking at the stigmas.