Yeah, I'd say khaki shorts/pants or dress jeans and some type of collared shirt (polo or button-down) for men. I would steer clear of t-shirts though.
Women are a bit harder though, I think it's because there are so many options of things to wear. I guess I would say the following would be fine (though not limited to): a sundress, button-down blouse, fancy top (there's so many different types it's hard to explain, but I think you know what I'm getting at), sweater, dressy knit shirt, polo, dressy jeans, khaki/printed pants or capris, or a nice skirt.
By the way, this is for the sigs, again park clothes are fine everywhere else.