What better billboard than the bumper sticker on the rear of your vehicle, passing before all those eyes following you in traffic, or backed up to the main door of your favorite coffee shop.  One innovative idea would be to place an assortment of wordings on each side of suitably-sized pieces of sheet metal with two holes spaced at exactly 15".  (plate size 4" X 15")  

This would facilitate rotating these plates, using wordings more poignant or passive, loving, etc.  They could compliment Mother's Day, election campaigns, or topical news highlights.

Can you imagine the controversy you would stimulate?  "What's abortion Mommy?" "What is pro-life?"  "Are you pro-life?"  etc, etc.  And oh yes, as for the two little holes in your car for the screws, I trust you will be richly blessed for this sacrifice for the defenseless unborn.