Idea of Prison Icon
A prison symbol consists of two horizontal lines and two vertical lines that run into each other, similar to a tic-tact toe board. Where the two lines meet, there will be another little line to show that the bars are tightly sealed. A prison is where prisoners are locked away, and would usually have metal bars to keep them inside.
This is a Prison icon. It is available in PNG and vector. Downloading is free for PNGs up to 100x100px.