Six Flags America has switched at least some of their frequencies to DMR. Here's what was found on Monday:
452.2125 [ ] (DMR - Color 3, Slot 1, Group 5)
452.2125 [ ] (DMR - Color 3, Slot 2, Group 6)
DMR with color code 3 was also monitored on 461.8625; this is probably also Six Flags. The license for these frequencies has not been updated with DMR emission designators. Six Flags has another license which expired last year.
The group numbers listed above may correspond to the previous channel numbers - Ch. 5 was Security, and Ch. 6 was Shows.