HOA Common Grounds

I distinctly remember in an HOA meeting last year we were told that ALL Common Grounds within Sage Creek where owned and controlled by Sage Creek HOA and that you could put garage and hoa notice signs up and the city of Wylie cannot take them down as that is not city property. Also, I see signs up in the center median at the west main entrance by groves all the time for garage sales, bunk beds?! for sale and then there is the guy on the corner by the school that posts 4 sale signs on his fence along with his tires!? OY!