For me, I normally buy these metal clips from Office Works:

1. You may have to trim down the width and length, depending on the size of your mesh holes
2. Bend the clip into a U shape
3. Glue (I tend to use the double sided tape from 3M) your badge onto the bottom of the U
4. Slide the clip through the grill and bend the legs towards the centre to secure the badge onto the grill
5. You may have to use a bit of double sided tape to stop it from shifting/being loose
But I found by doing this you preserve your badge and your grill as nothing is permanent.