I don't know if there would be any hard and fast rules.
Maybe if she was a 'cougar' type, she'd be pretty obvious and let you know and leave no room for deciding whether she likes you or not.
If she isn't the 'cougar' type then believe it or not, once we get older we don't have any different flirting techniques to younger women...the usual eye contact etc.
I know myself, I am finding the younger guy attractive at the moment, but I wouldn't pursue one just incase he wasn't interested in the older woman...so I am pretty shy.
Everyone is different.