Normal screws that hold license plate are used although I guess double side adhesive tape would work also.
My van, a 2003 GMC Savanna only allows for the top 2 holes to be used. I used a wad of this putty-like stuff that my wife uses to hold Christmas decorations in place. This just secures the bottom in order that there is no flapping or slapping under speed conditions.
My wife's Honda 1998 Accord has the "One Nation Under God" license plate frame on the front of the car. This is secured with all four of the pre-existing bolts for the license plate.