Mirror on a stick.”
It's a prison term for an illicit communications tool. In a row of cells in a block or a tier, it's possible for convicts to talk to each other, but not see each other. So they rig a piece of broken mirror on some kind of extending arm and stick it out through the bars when the COs aren't around (another thing you can tell with such a device).
About being given one-- a guess someone new to the house might be clued in about this practice and given a cheat by an old hand, as an act of kindness or an overture, presumably someone adjacent to the new man's crib, or no more than a couple or three cells away.
Any kind of figurative use of "mirror on a stick" is possible, but the original term means a kind of cheat, like a shank, or a curtain hook with a bent tip for picking small locks.
.
