Lookn for a place to buy 4- 6 Security Screws .... w/ tool 1/4 x 20-Fine w/ button head ..simalar to the one below
They are license plate fasteners, just check the license plate fastener area of you local parts store, Autozone has them,
1/4 20 is not fine thread ... 1/4 28 is ... Real common around prisons ... when I installed signs in the county jail ( I worked for the county for 30 years as a sign maker ) I always used the " Prison Proof " bolts. I usually used 5/16 18 NC ... a good bit stronger than the 1/4 inchers ...