What does "PLACED IN ST/SP CUSTODY" mean?

ST/SP is also referred to as protective custody (PC). This is a type of imprisonment to protect a person from harm, either from outside sources or other prisoners. Sometimes it is the administration that decides, other times the inmate asks for protection. This is isolation or solitary confinement, not necessarily a "punishment" but a safety concern and it's for their protection.

Jail and prison officials must know of the signs and characteristics of inmates that may need protective custody. Inmates such as first time offenders, young offenders, transgender offenders, or high profile offenders are all inmates who would potentially qualify for PC. The reason is these types of inmates are at a higher risk of being harmed or killed by the inmates because of their status or orientation. Also celebrities or ex law enforcement officials may be placed in protective custody.