Temple is a place of worship, a place for people to learn dharma, to seek for help, to serve others and to find a spiritual guide that will lead us to enlightenment. Not a place to spread wrong information and discourage others from doing practice of their choice. A temple should welcome everyone, irregardless of his or her religion or practice.
If DS is a spirit, and a DS practioner coming to temple, followers of the temple should welcome that person. Only when people come then only have chance to help. Doesn't people of this temple have compassion to help those "in trouble"? Shame on them to put up such a notice.