Those are clovers. It's a weed, but there's a small chance when you pull it out that you'll get a four-leaf clover that increases your luck when you wear it.
Clovers are weeds, but they do not make your town "quality" worse like the normal weeds does, if you pick up a clover it breaks, but there?s a chance that you get a four leaf clover, I usually don?t pluck them because I like how they look.
Even though they're classed as weeds, they still appear with beautiful town. I love how they look, especially in autumn.
Off topic: ForgottenT (Mark) I love your signature!