Yes, we welcome sinners, but we do not promote those lifestyles or encourage them.
So we ought not to pretend that we support sin in our lives when Christ paid for us to be victorious, to reign in life. We are changed, made into a new creation. So while we embrace sinners, we are also realize that God gives us victory.
Like in my jest, are we to then start putting up other symbols representing sins that we will 'embrace?' Yes we are all sinners, but hey, God can give you victory and allow it to not dominate your life by His grace. I get that they are trying to not condemn people, or alienate them away from the Gospel (that is commendable), but you don't put up a flag in support of a particular sin. Maybe they should get a pole out in front to support strippers (figuratively?) with a keg of beer on the side in support of drunks?