Baptism is not a "rule". Its a covenant and commitment between parents, sponsors, congregations and God.
Any one of those parties mentioned can refuse the baptism.
This signature issue is utter sillyness...it cheapens the sacrament. The baptism should not be refused, the child should be brought in to the church without its "parents" and get baptized. The act of baptism is not represented in the piece of paper you get.
The Catechism defines what constitutes a valid baptism. Among other things, either a father's or a mother's consent is necessary, unless there is an exceptional circumstance. The consent is then a part of the sacrament and any tinkering with it, such as a male presenting himself as a "mother", or a female presenting herself as a "father", or there being two "mothers" consenting, or two "fathers", will invalidate it. It is very good that these people want the children in their custody baptised, and there is a way for them to do so validly: have a real mother or a real father take the sacramental part, and the partner be a witness to it, or maybe a godparent.
What I suspect is really happening is that the gay activists want to smuggle a recognition of their bogus "parenthood" through the back door.
It seems clear to me, "Yes we will baptize the child. No, you cannot both pretend to be it's parents in order to advance your perversion and sin".
Infant Baptism requires the solemn promise by the parents and sponsors to raise the child in the Catholic and Christian faith. Two homosexuals living in an active homosexual relationship would, it seems to me, have trouble honestly making such a promise. I do not understand why Cardinal Ouellet did not emphasize that aspect, but that may be a subtext behind the "signature" issue. Even on the face of it, however, the Church cannot accede to an act that gives credibility to homosexual marriage because the Church insists that no such thing as homosexual marriage is possible. Baptism of a person not able to request it on his own (infant baptism) is not automatic upon request but can only be granted under certain conditions. Baptism comes from the Church as authorized by Christ, so it is perfectly appropriate for the Church to refuse baptism under certain circumstances. An adult who is living in open and obvious sin would be refused baptism unless and until he repents of his sin; in infant baptism the "parents" and sponsors come under the same requirements because they are standing in for the infant who cannot himself choose baptism.