Preaching doesn't have much to do with sexual orientation, except that certain sections of the church have got the whole church a bad name by their homophobia and transphobia. In that sort of context my "message" is that there are churches that welcome diversity.
Yes, that flag is for transgender people. I'm one of the less usual ones because I was always heterosexual "before", and after a period of wavering I think I've settled down to be heterosexual now.