I would think that a note or message written on a piece of paper the size of a cheque would send a better message and assure that it would be read.
However please remember that much of the money donated goes to good and worthy causes and these should not be ignored. Give freely to the Society of Saint Vincent dePaul or another great charity.
My youngest daughter lives in the Archdiocese of Milwaukee and has a "gay-friendly" parish priest. She sends her tithes to Priests for Life and to EWTN.