Police don't even trust Amber Portwood with a pen -- this according to a letter the "Teen Mom" wrote from inside jail, claiming cops are only willing to give her a special flexible writing utensil ... designed to prevent stabbings.
Prisoner-proof pens are pretty standard issue inside the clink ... but according to Amber's letter -- obtained by TMZ -- she's still freaked out people think she's a danger to society ... and she'll end up in prison.
Amber writes, "I don't think I'll ever take this sh*t for granted. I'm really scared I'm going to prison ... All I think about is Leah and how she needs a ro-model (sic)."
She adds, "I am a good person and I pray that I can change my life."
Amber wrote the letter to her brother last month -- after she was thrown in an Indiana jail for drug possession and failing to provide a urine test (a stipulation of her probation).
She's scheduled to appear in court on January 27 for her probation violation hearing. She faces two years behind bars.
Jailhouse Letter to Brother:
Cops Are Afraid I'll Shiv Someone
1/10/2012 12:30 AM PST BY TMZ STAFF
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